Both programs have their strengths, weaknesses, and bugs, and you can produce advanced designs with either one. But IMHO Altium automates or simplifies a lot of things for you, such that it’s easier to get there. On a really small, simple design it’s not a big deal, but with anything vaguely complex, Altium’s rule-based design works better. The flip side to this is that if you don’t understand the rules and how they enforce things, you will get frustrated trying to outsmart them when you want to override them. So you really need to learn what the rules are and how to “debug” them. But once you do understand them, and start using them to support your design intent, they facilitate things enormously, by automating things for you, and by preventing mistakes.
The other thing that bugs me about KiCad is that there are still many things that cannot be edited on multiple items simultaneously, requiring you to repeat the edit individually for each item. It’s improved in recent versions, but not enough.
And I’m not thrilled by Altium’s embracing of cloud BS and subscription licensing. I just hope they don’t jump on the AI bandwagon…