In 3.0/3.5 D&D multiclassing was discouraged by an XP penalty. Players were all about the PrCs instead because they were exempt. Typically you did not allow players to take multiple PrCs because you were supposed to have a story/quest requirement for each of them. It didn't make sense thematically to join multiple secret elite orders.
PF gets rid of the penalty so there's no reason not to do it, but I've still never seen 3+ "dip/splash" multiclasses in any tabletop game I've played in, though I'm sure some groups allowed it.
Even so, there's almost no multiclass in vanilla 3.x as good as a 2e Mage/Cleric, which was supposed to be balanced by level limits (that no one used). D&D was never really a balanced system to begin with.
There's also the issue of carrying over older mechanics without really thinking them all through. Consider that fighters in Pathfinder are still using the same hit die since 1e (d10). The only increases in health since then has been the change from 9 max hit dice to 20, as well as easier gains to CON, but it still means a 3.x fighter has roughly the same HP gains from levels 1-10 as an old school 1e fighter. Meanwhile damage goes up in every edition, from 3.0 to 3.5 to PF, everything keeps hitting harder. In Kingmaker they beefed up enemy stats even more while mandating a strict 1/2 hit die HP gain, so you get the recipe for 'Rocket Tag Xtreme' so many players either love or hate. There's simply no option here to build an HP tank, your health is just a tiny buffer between one or two hit kills.
Owlcat were taking ideas from JRPGs and MMOs but seemed to forget those games have much cheaper healing resources and deeper HP pools, as well as player-directed level grinding.
I see this pattern emerging again.
Most of us are noting the pattern of russians having oddly low standards in game design.
No, he's a straight up Mystic Theurge, just like he was likely designed to be given his 16CHR
I find this doubtful, Charisma does have utility for pure clerics; what happens when you turn on his auto-leveling?
I think there is a disconnect between different players. Consider there are popular builds for this game which are straight-up bad for the first 5, 10, or even 15 levels. Mystic Thuerge is notable for hosing your character for several levels, taking a long time to catch up. This is considered an acceptable tradeoff for endgame power to min/maxers, but not so much to normal players. Also there are people who build purely to exploit high skill check XP in various ways, or who "grind solo in old sycamore until level 10" or other silliness like that.
It reminds me of Wizardry 8 discussions where people claimed maining a class with the Locks and Traps skill was bad because you could multiclass into them for one level and click on the 8-tumbler lock in Arnika for 4-5 hours to max out the skill. If that seems reasonable to you then we're just not playing games for the same reasons. If you're willing to go to such extreme lengths to break the game, anyone complaining about difficulty would seem like a whiner.
I doubt when a normal player puts a cleric or mage in their party they do so expecting to have a front-line melee powerhouse (the player has no way of even knowing what spells are in the game until they reach the required level). The fact you can turn spellcasters into multi-role combatants speaks to the versatility of the underlying system (and D&D's perennial OP spell list) but expecting this from players is deeply unintuitive, pretty much regardless of genre.