I agree with this statement.

However, we're not talking about a complete copy, but rather using some of the existing developments and technical details. In my opinion, the option to choose a hero class has great potential. In this regard, Heroes 3 is better than Heroes 5 (there are 2 classes per race, while here there is only one, without a choice).

All heroes have the ability to upgrade almost all skills in the skill tree (there are very few truly racial skills). This implies that there is no need to use classes, but if you have a large number of heroes (for example, as in the NHF mod), then dividing them into 2 classes is good (which, in principle, I wrote about above).
Let's assume that we also want a mage or a warrior (classes). Some magic is purely general (for mages and warriors) - light, darkness, while some is only for mages (summoning and chaos). Sorcery is purely for mages, and the rest of the non-magical skills are suitable for everyone. Having only 3 pure magic skills results in an incorrect rotation for a warrior and a mage. Therefore, tying it to stats is pointless (like changing them in different classes). The skill tree was not designed for these classes. And they even added a mentor...
1) Let's assume that academics will have a mage and an alchemist. The first actively uses all schools of magic, while the second, for example, supports units by upgrading attack and ranged attack (mages have 3 ranged attack stacks!), and focuses on synergy instead of sorcery. Where is the alternative? The alternative that existed before classes will simply be available for each class.
2) Humans. There is not much magic available for them. Should we not give them a lot of spell power and chaos? They are not destroyers. Then let's divide them into a light warrior and a dark warrior. Again, we limit/reduce the ability to choose with the development of two schools. There is a choice of being a warrior (almost without magic) and a paladin (for example, light magic is a priority), but here it's even sadder...
In Heroes 5, the race acts as a class. In the Creature Builder, for example, there is a choice of class, but not of race.
It is much more important to choose for yourself as the game progresses what you want to become, rather than deciding this at the start!
But even here there is a solution. We need to find something that can really be used to divide into classes. But it won't be skills or their probability, or the relationship of these skills to stats.

By the way, dwarves have the opportunity to be divided into classes due to the presence of rune magic. Ten runes and their enhancements are enough to be distinguished as a separate class.
But we can also come up with 2 such classes for dwarves: a blacksmith and an engineer. A blacksmith can improve artifacts, modify them, and find them where it would seem they shouldn't be, while an engineer can improve machines, mines, and castle towers, and lay explosives. This is just an example and should not be taken too seriously.

3) So, a human can get light and, for example, summoning (just for example), while the stats for magic and knowledge will be higher. But then there is the problem with the castle. Where can you get summoning? And there is no need to say that "on the map". This would be unfair to the other class.
But problem 3 can be solved in an unusual way. Cities can also be divided into classes, and each city of a race can be given completely different native magics ;) I chose a human hero who specializes in summoning - I got a city with the necessary native magics. This is quite interesting, considering that summoning can be useful for humans in the early stages, especially with the presence of the Amulet of Elements or the Phantom.
But the possible solution to problem 3 contains the old one: the imposed accuracy of development. So, perhaps we need to think in a slightly different direction.

4) In the mod, for example, there are magic suppressions. If they are used, then it is really possible to divide into classes. But I wrote why they cannot be used. One excludes the other.

P.S.

In this regard, Heroes 3 is better than Heroes 5 (there are 2 classes per race, while here there is only one, without a choice).

Dividing into classes in the fifth Heroes game, based on the principle of the skill tree, actually deprives us of choice ;)