The fact that just few areas had higher respawn rates IMO confirms that it was intentional.
I've managed to explore those Ruins without cheesy tactics in my first playthrough, almost 15 years ago, when I wasn't an experienced player yet. It has been difficult, but very rewarding in the end
Erhm, but you go to the BG1 game and go to the map, you see that it's not actually a "respawn rate", it's a respawn point that has a millisecond respawn rate, so every time you do not see the point in the area map, the monster respawns, and as the area is a dungeon, the creature can spawn multiple times in the point cause you lack the capability to see the point as you should be walking through the area with a full party.
Yes, I remember that I always set a guard(a character) to a point in the dungeon so the dogs wouldn't pop up from no where too... it was a pain in the behind.
So the alleged respawn rate you are after is actually a bug in the original game. The BG1EE didn't want to recreate that so they set the rate to a practical number which then makes the area a lot easier... see ? Yes, they could increase the spawn points/number of creatures per point, and thus make the dungeon a little harder, without the actual bug that was in the original game... but that's not what you are after, is it, but the buggy behavior.