I also haven't purchased the sequel but I did spend good amount of time on the first game. At least the original KCD was noticeable different in comparison to other more popular and prominent RPG's, which in general are quite a bit more fast paced and action oriented. Just as an example: I spend several days in KCD to just learn how to read so Henry could understand alchemy recipes better and after that, the next mundane task was to sneak every night to local villages apothecary shop to use the alchemy bench to make potions and before sunrise sneak away without anyone noticing the player. If people expect some power fantasy then they might not like it, since major part of KCD charm is how slow paced and tedious (partly by design) the game is; In Witcher 3 and Skyrim you slew dragons - in KCD you are relieved if you don't get overwhelmed in 1 vs 2 fight. I forged the review about KCDII but gist was how the game isn't your typical fun RPG romp but great medieval sim RPG, which sums up my feelings for the first game - for all of it's flaws I'm glad that the original game sold well and it's nice to see how the sequel is seemingly having it's Witcher 2 -esque moment.
Yeah, most people overestimate the impact that combat has on game sales.
"Skyrim has shit combat" --> sells tens of millions of copies
"The witcher series has shit combat" --> sells tens of millions of copies
"Kingdom Come has shit combat" --> sells 8 million
"Fallout 3/4 has shit combat" --> tens of millions
"Final Fantasy 16 and VIIRebirth have awesome combat" ---> sales disappointment
"Dragon Age Veilguard has great combat" --> bomba
(I am going with hearsay here, because I didn't buy those games because of ... the combat system)
It is quite hard to name sales disappointment with good combat if you hadn't played the game, because the fanbase of said game who proclaim the combat great isn't either the most objective about it, OR is objective about it but they are a niche audience who likes such combat and other find it bad.
In those big RPG games, the combat is mostly a smaller part of the whole. What those games NEED to sell millions, are great RPG systems, immersion, story, dialogue, quests, etc.
But it also depends on the type of combat system. Anything Action combat, for me, is the lowest part of the totem pole overall. Like Witcher, Fallout, Skyrim, etc.
On the other hand, strategy or tactic type combat is, while not the biggest draw, very high. Games like Baldurs Gate 3, XCOM, Total War, BATTLETECH, etc.