If we are talking about useless skills, I would choose these:
1) First Aid. At the start of the game, the skill is useless because the tent heals more than the maximum HP of available creatures even without the skill. In the late game, the skill is useless because its effectiveness is incomparable to the damage dealt by existing stacks. It can only be useful in situations where, after every turn, the first unit in a fat flagship stack has about ten hit points left (in other words, slightly less than never).
Proposal for making tent mastery useful:
Without First Aid, the tent heals as it always did.
With Basic skill, the tent casts the "Cure" spell at basic level congruent to Magic Power 3, in addition to the existing heal that is unchanged for the current basic level.
With Advanced skill, the tent casts the "Cure" spell at advanced level congruent to Magic Power 3, in addition to the existing heal that is unchanged for the current advanced level.
With Expert skill, the tent casts the "Cure" spell at expert level congruent to Magic Power 3, in addition to the existing targeted heal that is unchanged for the current advanced level.
Healing does not work on magic immunes - the tent affects them in standard mode. The same applies to those immune to the water school. If a magic/water immune is chosen as the healing target, the cure spell will not work at all (since they cannot be a target for this spell). When using the tent on a water-magic immune, it will be processed by the tent's standard targeted heal.
A Cloak of Silence or a red orb blocks the First Aid skill, and the tent works in standard mode (only targeted heal works).
What this leads to: the possibility of useful use of this skill in PvP, as mass healing will remove harmful effects (including blinds, oil, etc.). From an outsider, first aid will become close to a must-have skill.
Giving the tent the ability to resurrect killed units in a stack is non-atmospheric imba. If you bring a corpse to a field medic, it remains a corpse - but giving a practicing, upgraded medic the ability to cast kind healing spells is acceptable.
Rion, Jem, and Verdish (FA specialists) will:
1) have a tent from the start;
2) increase the power of the cure spell congruent to +1 SP for every three levels.
2). Mysticism. Absolutely useless for both warrior and mage. Only a lazy person would fail to build a Mage Well on a good template.
However, the skill can be made much more useful.
Without mysticism: the hero restores 1 spell point per day.
Basic mysticism: the hero restores 2 spell points + 2% of maximum spell point reserve per day.
Advanced mysticism: the hero restores 3 spell points + 3% of maximum spell point reserve per day.
Expert mysticism: the hero restores 4 spell points + 4% of maximum spell point reserve per day.
Thanks to such a change, the skill will be useful even at the start of the game for a starting mage (allowing them to be less dependent on wells and cities with guilds), adding mobility to the mage. In the late game, it will also be quite good (better than now: a hero with 40 knowledge will restore 20 spell points per day with expert mysticism, rather than 4 as it is now). The difference is noticeable.
Mysticism specialists will receive +1 restored spell point and +1% of the possible maximum for every 7 hero levels.
3) Eagle Eye. This is one of those skills that makes you want to cry upon seeing it.
Proposal: strengthen Eagle Eye by giving it fundamentally new capabilities while leaving the existing combat functionality intact.
Basic Eagle Eye: Ability to view spells of level 2-3 in a level 1 Mage Guild without building levels 2-3. Resources for the 2nd-3rd floor of the guild appear quite late - but using this knowledge, the player can plan further game tactics.
Advanced Eagle Eye: Ability to view spells of level 2-4 in a level 1 Mage Guild. Similarly.
Expert Eagle Eye: The same, but levels 2-5.
What will this lead to? To the ability to better plan the magic strategy at the start of the game. To the ability to avoid unnecessary resource spending in the late game - if you check the MG in a captured city, it will be immediately clear whether you need to spend another 20-20 ore-wood and 28 rare resources each for building levels 2-5. Of course, no one in their right mind would take this skill as a primary - but for a noob, it will always be exceptionally pleasant.
Furthermore, with the planned expansion of the spellbook with new spells, variance will increase. Having a noob with good Eagle Eye will provide better orientation.
As an option for how the skill works: show the spell in a pop-up window when right-clicking on a collapsed scroll. Doing it like in VoG (I don't remember what handled guild viewing there, honestly) is bad tone.
Eagle Eye specialists will have the same bonuses as they do now - no need to reinvent the wheel. Eagle Eye artifacts will not lose their functionality (although we admit they remain trash).
Throw tomatoes, comrades. If I am wrong, I would like to hear constructive criticism with arguments. At the same time, the argument that "this was already in VoG/Heroes 7/The Simpsons" is not an argument, IMO.