Grando
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I'll try to elaborate on Dirty's idea – there shouldn't be weak skills.
Instead, there should be skills for the main hero and skills for support heroes, and even support heroes should vary.
For example, in Warcraft III, I usually level up a support hero with Immolation and Ignite to the expert level (or at least try to), which makes it a great skill for a secondary hero, just like Scholar is very useful, but not for the main hero. Fire magic isn't always leveled up on the main hero (especially if there's scouting), but leveling up a secondary hero with a decent Town Portal is also a must-have.
So, it's not about having weak skills, but about having strong skills for the accompanying group, and these support skills should also be powerful.