It's not like I'm talking a lot about what to do on the quests. I'm too old to remember the details, especially the map layout. What I do remember is the threat level in the quest (trap heavy, type of boss monster etc.). That means we can prepare better and not be wiped out easily. The worst that happens is when we play in our 2 hour session and spend most of the time moving back and forth to the quests because we die all the time and must respawn.
The only quest lately we've played that I have played before is the Catacombs series. Since some of the later monsters are wraiths that you can't hit unless you have ghost touch weapons then it's good to know this in advance so we make sure we have at least one such weapon. Ghost touch weapons are needed in several quests (like the Delara's tomb series). As a matter of fact you should keep all weapons with special abilities since they're quite rare and you need them in some quests. E. g. blessed, good or holy weapons are needed against ghostly skeletons and some other monsters in Delara's tomb.
This is not a complete spoiler because the type of monster to expect is shown in the login screen to the quest. E. g. a wraith is shown in one of the catacombs quest logins. Most info about monster abilities can be found in standard DnD, but DDO has made some variations that we have to learn the hard way (like ghost touch weapons needed for wraiths and spectres).
I've played in some (not too many) PuG's and it's very normal there that the experienced player (one who has been in the dungeon before) gives some general ideas about what to expect inside. Is the dungeon trap heavy, do you require specific skills or items, what kind of tough monsters you can expect etc. This is often done before we enter the dungeon so people can get what they miss. The experienced player is the one inviting to the group and he knows which classes to look for and invite. So in most PuG games you have others who know the dungeon when you enter for the first time. I think that's fine because then I have a lesser risk of dying there. E. g. if the quest is trap heavy and I'm moving in the front then the group leader tells me that this will get me killed unless I'm careful, just like a particular rogue in our guild usually tells me.
Besides having some info ahead of time I see that many players rush in the dungeon and trigger traps that kill them etc. Level 5-7 quests often have traps on the chests or plot items. Some are really nasty like a gate falling down close to the chest and spawning lots of monsters when the quest is open. Then you have to fight all the monsters alone and you will probably die.
I've done my share of dying in DDO and it's not particularly fun, especially when the entire group is killed and we need to keep a PC inside while the others respawn and re-enter. When you only have 2 hours to play you want to accomplish something (like solving at least one quest). So having wipe outs is not fun at all, especially when they could have been avoided with a little more knowledge about the particular quest. E. g. the proof is on the poison quest is a particularly nasty one that we died several times trying to solve. Our group gave up on it, but I managed to solve it in a PuG with an experienced group leader who had been in there before. Timed dungeons are also frustrating unless we're well prepared and know what to do.
I also remember having played quests that a certain sorcerer had played before and we were told what to expect and where to go. That's normal and it means we use our time more efficiently when we play.
What's not fun is to rush through the dungeon just killing everyone in sight because you know you can do it. That means sorcerers and rogues become useless. All characters should have a chance to shine, like the rogue looking for traps etc. This behavior is typical when you repeat a quest just to get some extra XP because you know the layout and can play on instinct. But we play so seldom so we don't repeat quests. If we do it's because we play with our alternate character.
The Catacombs is a bit special for us because it contains of maybe 7 parts or so. What has happened is that our main characters get to chapter 3 and then a new character arrives who hasn't done chapter 1-2. This means our main characters must dump the quest advancement and restart the quest. Then it's quite normal to rush through chapter 1-2 to get everyone up to chapter 3. We were intended to play chapter 3 so I don't think that's wrong. But this is typical for guild play when we don't have time to finish all chapters in one go. Getting out of sync in quests with chapters is quite frustrating. So it might be that you remember these rushed sessions of chapter 1-2 of the catacombs and don't like that. But we've only played the last chapters once in the guild.
The quests I've played with PuG's are quests I haven't played at all with you, like Delara's tomb. You can get 10-15k XP from that series and you can do it in maybe 3-4 hours. The end loot is excellent too.
We've played Catacombs, Tangleroot Gorge and Shan-To-Kor the last months. Neither of these quests have I played with PuG's. I've done Shan-To-Kor with you and played Tangleroot and catacombs solo with my paladin. My cleric is doing these quests with you. I tried to do catacombs solo with the cleric, but died and had no chance to complete it. But it was a long time ago so I don't remember the detail about these quests. I think I was only level 5 when I tried to do them solo.
So I don't think it's a habit in our group to tell others what to do just because some of us have played the quest before. We're all too old to remember all quests anyway and most of us are too lazy to read the quest hints at wikipedia. Getting general info about a quest is not bad because that allows us to prepare for the quest to avoid wipe outs. Playing DDO is fun as long as you avoid having the entire group being wiped out in the dungeon. Many of the level 5-7 quests are potential wipe out quests so you have to know something about what to expect to avoid it. E. g. some of them are very trap heavy, some require you have a special character type or item. Wouldn't it be silly to not be able to solve a quest because we didn't have a rogue or a ghost touch weapon? Having spent 2 hours of our precious playing time just to leave the quest with no XP and a future XP penalty for re-entry is not what I think is fun.