Well, if I switch to playing against the computer like that, it will just kill my interest. I used to play some scenarios and complete them in 40-50 days without knowing any cheat codes, and that was fine. But now I feel ashamed of such results.

There's absolutely nothing to be ashamed of. My son comes to visit, and we play hotseat together, forming an alliance against the computer. Or my good friend comes over, and we do the same – play hotseat, forming an alliance against the computer. Of course, there's no talk of records, and the playing style is completely different from tournament play. These are just different things.
You're probably a chess player, maybe with a first-category rating or a candidate master title. But the mindset is completely different when you sit down with a friend to play blitz or when you participate in a serious competition! Offline tournament play is compared to a chess composition, where you need to achieve a certain result (checkmate, draw) from a given starting position (save). That is, playing "just for fun" is great; it's just that in tournament play, this "fun" is of a slightly different kind – perhaps like polishing a diamond. But one doesn't negate the other – many "very serious" chess players love to play blitz.
By the way, even in tournaments, there are online and offline versions. It's true that you can only achieve great results in both cases if you know the map well.
P.S. We have outstanding programmers on our forum, for example, AlexSpl. He has started working on a high-quality random map generator for the second Heroes game. If he succeeds, it will give a new impetus to online play, meaning you can play a new, unfamiliar map (the feeling of being a pioneer) against an opponent who also doesn't know it! I think it should be very interesting.