Hussar
Legend
Heh. See, that's where play experience comes in. I've played KotB back in the day and much later as well, and not once was it ever done as a "sneak in, find allies stealth mission."Except I think the experience of playing Keep on the Borderlands under Basic rules or AD&D 1e/2e plays a lot differently than under 5e. The intent of KotB under earlier rules was that you had to sneak in, find allies, and treat the entire cave system as a stealth mission and do lots of hit and run because there was no way PCs at that level could take it on directly. 5e would take that same adventure and likely turn it into a heroic “storm the dungeon” adventure and perhaps a bit of a slog as a result. It will be interesting to see how the new adventure on KotB that they’re releasing modifies the original.
For one, AFAIR, there are no allies in the caves to speak of. And, one of the bigger changes in playstyle is party size. Basic/Expert or AD&D were both based around a group of 6-8 PC's plus NPC's. You weren't overwhelmed by enemies in KotB. Those were mostly on par encounters. Well presuming that you didn't go into the wrong cave of course.

But, it was easily possible that your AD&D group had 10-12 characters (between PC's, NPC's and various others) plus pets and whatnot. That's, to me, where the big change in playstyle has come in with WotC D&D. The presumption of a MUCH smaller group. A 5e group is generally 3-5 characters and that's what the game presumes.
And funnily enough, I think you have it exactly backwards. The Basic/Expert or AD&D group storms the dungeon. Why would they bother with stealth? Virtually none of the characters could actually be stealthy, since there were no rules for most characters trying to be sneaky. And, it was easy to have a 1st or 2nd level AD&D PC with a 1 or 2 AC, meaning that the baddies basically needed 19's and 20's to hit you and generally only did 2-4 points of damage on a hit anyway. Add in ranged weapons, where your bows got 2 attacks per round, and you could mow down the baddies.
5e is FAR more lethal than AD&D at those levels if you use AD&D numbers against 5e characters. 10 orcs will obliterate a 1st level 5e party. That wouldn't be a speedbump for and AD&D party.