Well it has been a long time since vanilla wow so my memory of the way the different specs broke down in terms of dps may be flawed, but I was also the #1 rogue DPS in a major guild, and I was one of the first people to work on a rogue spreadsheet to determine how much every stat point was worth on average (although the later rogue spreadsheets that came out were way better then mine). So I definitely know what I'm talking about and what I can tell you was that there was always almost always a mathematically superior build, even if the math did vary a bit by encounter. You didn't necesarily HAVE to follow the build, I was generally a bit of a rebel myself and sometimes took builds I enjoyed even if they weren't always the top dps specs and it didn't stop me from being #1 because I was a good enough of a player. But there was almost always clearly a most efficient build. You can go to a site like elitist jerks now and read incredibly detailed mathematical breakdowns of dps specs, done by people whose mathematical prowess I am in awe of, and who are widely regarded by the community as being the experts of the specific classes. And it almost always boils down to "if you want to play this spec, this is the exact talent point build you use". Sometimes you have a couple points to play with, but the number of options is rarely significant. You can break away from the best talent build if you want, but it's always with the understanding that your dps will be lower.
So yes I understand that back when you were playing there were a lot of people with a lot of bad opinions. The community and the math has evolved greatly since then and it's now MUCH easier to find recognized experts on classes and builds. So don't assume that I don't know what I'm talking about just because in your day you encountered a lot of people who didn't.
Edit: Oh and in terms of players determining your identity in WoW, well it's still not great, I don't think it's any better or worse. Pretty much every spec is viable now which helps for a little identity because there are more options. The classes are a lot more complicated to play then in vanilla days, so people tend to stick with a specific build despite the easy option to switch just because it's frequently hard to master a new build. But as you say WoW has never been great about character identity.
First of all, I apologise for assuming you were ignorant - but it wasn't based on the fact that I've met a lot of people who were - but on what you said, which I still consider blatantly false.
But I see now that you have significant knowledge about this - and we simply disagree about it and maybe it's about perception more than anything. That's ok, I've had countless debates with countless competent rogues about the same thing, and some of them actually knew quite a lot themselves.
The issue with EJ (yeah, I spent countless hours there myself) and theorycrafting like it - is that it's based on math and static encounters - and is mostly about what happens during a raid. I won't deny that there is a LOT of useful information that you can use whether learned or not - and it WILL help you perform better, if you take the time to understand it in-depth.
The thing is that people are not just raiding, and during raids - they're not just DPS'ing - even as rogues.
It's true that if you could predict everything from gear setup to buffs (buffs worked VERY differently in vanilla), to exact encounter setup and playstyle - you COULD find a build that would perform better than others, but you can't - and you never could. Back in the day, getting your hands on a weapon like Thunderfury - could totally skew the numbers - and the "top build" was combat daggers back then. That weapon alone could make combat swords the most efficient one - especially if you had access to Windfury buff and so forth.
Yes, it's true - that for every "gear setup" - there will be an optimal build for PvE raiding during static encounters (as in, you mostly get to fight it from the back without too much shit going on around you), but not for PvE 5-man dungeons, and most certainly not for PvP arena/BGs. You can't "trivialise" those parts of the game, because they're HUGE - and lots of people don't even raid in the first place. So, the fact is that there are MANY builds that are viable for many parts of the game. For PvP alone, there must be at least 5 VERY different builds that are all a part of top-end arena play.
Another vital point that so many people overlook when they come up with this claim that "you can just look up the perfect build - and choice is irrelevant" - is that it has taken YEARS post-release to come up with this math, and to figure out what happens behind the curtain. Blizzard have changed everything several times over, and in the past - everything was much more opaque than it is now. So, even if there was a single perfect build available for all situations - it would still have taken years to arrive at it. I hate to break it to you, but people are playing the game during those years - and while they're waiting for the theorycrafters - there is lots of experimentation going on that's FUN. Exactly like Magic the Gathering was incredibly fun for the first 3 years (before the real Internet revolution), before everything was analysed to death and became available on the net for all too see.
The issue with "math people" - and I'll readily admit that there were some pretty amazing high-level dudes on forums back when I was playing, is that they tend to exclusively focus on the predictable - and forget the actual game, thinking they take everything relevant into account when making those Excel spreadsheets. I was raiding with a few people like that, and they always ended up performing much below me, because they couldn't think outside the box - and they forgot that actual movement and a constant awareness of the environment meant just as much in many scenarios. I'm not even going to get into how they perfomed in PvP. There are no optimal DPS cycles in PvP. Naturally, not all mathematicians are like that - but that's the trend I noticed with people obsessed with numbers and the idea that you could figure out everything with them.
Anyway, this could become a very long debate - and given your level of knowledge, I think you know that what I'm saying is true - even if we disagree in terms of conclusion.
If you still insist there was a "top build" in vanilla for everyone to simply look up, and that it's always been there - then we simply disagree. It might be about perception, but I most definitely don't agree with that. I'm sure the way Blizzard have handled the game in recent years have made it much more accessible, and the "top builds" more "top" - but I'd bet my life there's still unpredictable encounters during raids, and lots of PvP with lots of builds.
So, unless Blizzard does something to change this concept of skill-swapping at will - I think the game WILL suffer for it. Exactly like I think WoW has suffered greatly from being turned into a giant instanced candy-dispenser with dual-speccing and narrow tree setups.
I know a lot of players are happier that they don't have to work to get gear and worry about their builds - but I'm not convinced they wouldn't have been playing the game without these changes, and I'm not convinced they actually know what's the most fun for themselves in the long-term.
The work/grind has simply changed from getting the first epics to getting the "new epic" every 10 minutes. People are still on the hamster wheel, it's just a lot more blatantly streamlined and predictable.