- What are the drawbacks of Heroes 3? (What didn't you like about it?)

In principle, there are a few (not many) skills that are not very useful, but everything depends on the comparison. And if there were no cool skills, then mysticism would be great. You choose more useful skills, but you have to take what you get. It's like in cards - you expect to get 4 aces in a draw, but you get 4 sixes. And you would probably like the deck to consist of only aces - but then the opponent would also get only aces...
"attack is much more beneficial than defense," especially for a pushover (tank), who everyone attacks:D. This can only be useful for a gray hippopotamus who doesn't care about the enemy's defense.
Magic power is very useful if you want to, for example, kill a diamond golem with its 95% resistance with a single lightning bolt. Especially if a mana vortex is placed near each enemy unit. But what if there are no wells on the way, and the warriors are not very intelligent? By the way, as far as I remember, the problem of playing as a mage is precisely the shortage of mana, which needs to be replenished often, and not the power of spells. After all, cloning 1 angel and 10,000 angels costs the same. And it can be destroyed in 1 round, although there would be enough strength for 50.
Everything depends on how you look at a particular problem. And on the ability to get out of a difficult situation, and not to adapt the situation to yourself.

I have analyzed all these points - probably in the way a game analyst should. That is, with the involvement of mathematics and a probabilistic approach, and not a situational one.

In particular, I have thoroughly analyzed everything related to Attack vs. Defense. I will not provide the analysis of the dependence of the benefit on the parameters of Defense or Attack here (although it is interesting), by the way, if anyone remembers, for Attack +1, you get +5%, for Defense +1, you get -2.5%. But this is just for the record. The main thing is that most battles with neutrals (that is, in the development phase, and not only) occur in conditions of a significant advantage on our side, and our main task in such situations is to minimize losses. And in this case, the best defense is offense. A model example: we attack 30 gnomes, kill 20. The remaining 10 gnomes inflict damage on us, first with a counterattack, then with an attack. But if we had killed 25 gnomes immediately (only 25% more!), then 5 gnomes would have attacked us, and our losses would have been twice as small. This example well illustrates the thesis "the best defense is offense."
Yes, there are situations where Defense is more important - these are situations when the neutrals attack first, again, with a large advantage on our side. This is passing archers, flyers, just fast units. Taking Dragon Utopia, in the end.

But in general, according to the results of my analysis, my conclusion is that the balance between Attack and Defense should be adjusted. I plan to make it +4% damage for +1 Attack, and -3% for +1 Defense. At the same time, the ratings of creatures will practically not change, as well as the cost.

Added 16 minutes ago

3. The dependence of the hero's movement range on the speed of the slowest unit.
It seems - what's wrong with that? IMHO, unnecessary micromanagement - fussing with "boosting" heroes, which newbies are taught "from the cradle," is simply unnecessary. Why can't I take a hundred zombies or gnomes into my army? I doubt that the developers intentionally introduced this parameter into the game, or rather, I think that no one suspected that people would start using it in an attempt to gain an extra movement point. However, this is just my opinion, as I am not sure - in principle, it can be considered as an element of strategy.

Yes, you can treat this in different ways. As well as with chains. In my model, heroes will cost 5000. There will not be many of them in the players' possession at the beginning of the game, and there will not be chains either, and perhaps there will not even be micromanagement, or at least less of it. Closer to the end of the game, chains are needed less, with the increased mobility of the main hero (City Portal, etc.) and the accumulation of a large army that needs less small reinforcements of the size of a weekly increase. By the way, the City Portal will be slightly adjusted :)