Having mod support won't mean the game is better, of course. The game is what it is at release. Modding certainly can and usually does MAKE it better though. Can't think of any game since I've tried mods that I didn't think couldn't be improved by a few simple tweaks here and there.
DAII could've been "fixed" had it had anything like the mod support your "beloved" Bethesda games had. Sure the base games quality would've been the same but eventually a portion of the gameplaying population would've settled down as modders "fixed" and improved stuff.
Does this mean I approve of devs leaving to modders what they should've done? No. But it does mean I'm happier when fixing can happen. And even if devs could ship a bugfree game, mods can still improve/tweak gameplay stuff according to particular tastes.
I'm fine with mod support being released after the base game itself, but WHEN it's released isn't the same as whether it is better IF it is.