Wrath is better in basically every possible way.

Some of that has to do with being incredibly open from the first 30 seconds that the main enemies are demons/devils (rather than teasing out it is the fae) and that demons/devils are much more straightforward enemies.

Part of it is also that you get a… kind of really unfair power boost early on. Mythic Levels are not Epic Levels from 3e and you actually get them really early on (your first around character level 5 or 6) and they are kind of ridiculous. Stuff like getting a ridiculous number of extra spells per day, having all killing blows and crits with ranged weapons do AOE damage, doing AOE damage on the first melee miss of any round, etc. It gets REAL stupid and that is even before you start getting the really fun stuff like turning into a Lich or Dragon. Which helps a lot since a LOT of encounters are the “you do one of these per tabletop session” kind. And your entire party get the “only kind of ridonkulous” version, not just the PC.

And the encounter design in general is a lot better. I find that enemies care a lot less about AOOs and will just sprint past your frontline to beat on your archers. But there are also far fewer “Cool. You need to push through twenty endless respawning midboss enemies to get the summoner” fights. I totally don’t fucking hate that house at the end of time at all.

It is also worth remembering that Kingmaker is in rights hell and Owlcat and that publisher are not on good terms in the slightest. So they couldn’t even really go back and patch Kingmaker (whereas they did a LOT to improve Wrath post release). Which kind of shows with some of the Wrath tooltips bordering on apologizing for Kingmaker (stuff like getting rid of supplies for resting).

Kingmaker is one of those games that are “if you ever think you MIGHT play it, just play it first… but turn off fail states for kingdom management and read a guide”. Whereas Wrath is a genuinely amazing CRPG and has an argument for being the all time best.