ASW – Alternative hero leveling.

There's this option for upgrading units. The catapult should be enhanced with the "Ring of Machines" artifact or something similar.

It's an interesting option. But it still seems like additional links are needed from the ranged attack skill to the offensive skills + from the tent to the "Control Machines" skill. Like a clever tent.
Without these links, it might be possible to take both the tent and the offensive skills at the same time.

But then the problem arises that it won't be possible to upgrade all racial skills?

And why would you need to? Can you upgrade all the perks in defense at once? The point is precisely in the choice, and that's what makes it interesting.

Added 4 minutes later

The idea isn't without merit, but to talk about a significant advantage means lying.

Well, it depends. An alternative racial skill or a uniform racial skill (if you take 3 perks, you get them all at once) – in my opinion, this is a significant advantage. Imagine if there were only 3 perks to choose from in defense, but you could upgrade them all. Would that be better than it is now? The same applies to racial skills. The difference is that racial skills are always given at the start, i.e., improving them is even more relevant than improving defense skills.