You are absolutely right, it should be 1 skill only. We name builds after the one skill er use anyway, and since it’s just about spamming that skill, why bother having any other active skills?
*Sarcam off
Now do think about it? How many skills do you actually use? D2 often only use 2, a few builds 4. D3 mostly uses 3 skills.
The rest really is passives.
If a skill isn’t activate to gain a direct benefit from doing something on the battlefield, it’s just a passive. Warcry, Battle Rage, Storm Armor, Ice Armor and Energy Armor are examples og passive skills that’s made it to the active list for no reason.
It’s a matter of creating Active skills that actually do something and is worth the time to activate, rather than getting short or long buffs that just increase your character.
Look at your skill bars again and consider what skills you actually use to hit monsters or time in order to create some sort of combo. These are the real active skills. The rest is just passives acting as actives to folk up empty space.
And that is what D4 needs to improve, create true active skills worthwhile to utilize, and combine, and interesting enough to evolve while making meaningful choices.
And by that, 6 skills is plentyful.