I'm talking the games in their final state. Last time I played HoI3, it abandoned fronts (the Western front vs an allied invasion, when the Russians joined the war). Last time I played Darkest Hour, Germany tried to march straight over the Maginot and only had a chance because it had been buffed to high heaven (it had 200-300% its historic resources, and needed it, to achieve historic results). I can't recall my last game of HoI1 as I didn't try that last year (and haven't for many years), but I assure you that HoI1s AI was orders of magnitude worse than HoI4s!
HoI2 didn't frequently suicide-invade because it struggled to invade at all (when it did invade, it was generally just as suicidal). Neither HoI2 nor HoI3 could manage large invasions, something HoI4 does a lot better.
I'm not suggesting there's not plenty of work to be done with HoI4's AI, but rating HoI3's AI (tfh, 4.02) higher than HoI4's (1.3.2) requires rose-tinted glasses, blinkers fit for a draught horse or both. I don't mean this in a nasty way (sorry if I sound blunt, am a bit crook, takes my diplomatic edge off - your post was perfectly reasonable and am attempting to make this reply likewise

), am happy to go through AI and examples blow-by-blow - AI is the key feature in games for me, so I pay a fair bit of attention to it. Whether HoI4 is better than HoI3 is less clear, but to argue it's clearly worse is a 'brave' debating position to take.