In Endwalker I really want them to step it up with the new skills and spells. We're going to level 90. A mere 10 levels but that means something it terms of how far the Warriors of Light have come.
Machinist needs a sniper rifle attack or a bunch of drones they call in.
Summoner should get a new summon but it's hard to show up Bahamut and the Phoenix. Maybe Odin or Anima or the Magus Sisters.
Red Mage and Samurai should probably get counters. Like instant critical hits that land if someone attacks them or someone they're near.
White Mage and Scholar might benefit from summoning Angels to attack with when not healing.
Black Mage has really been held back in terms of all the spell it should have learned by now. No meteors or comets? Really?
Dragoons should have an attack like Sora's and Clouds from KH, Sonic Blade.
Astro could like use a magic counter. If anyone near them or they are hit with a magic attack, they rain light beams on them.
Dancer i can't think of much that would help them in terms of attacks. Maybe being about to pick two people as dance partners.
Paladins and Gunbreakers could use an attack that drags foes to them like rescue but used on foes. And they take damage as long as they chained up or trapped.
Dark knight could use a move where they summon shadows under the enemy for heavy critical damage once with a long cool down. That way if they're alone with no healer they can still end the fight quick.
Basically I'm saying there still lots of great ideas out there. So I dont wanna see some place holder filler skills that no one likes. A lot of Monks stills were like that for me. I started with it but I could honestly say it's still consider a weak class with few cool looking attacks.
If I had to add to it, I'd say make a follow up attack to Demolish. After you put Demolish on a foe, doing this new skill would cause heavy damage. Maybe an attack they dont have yet, like a lighting kick like Chun-li or a slam like Senel in Tales of Legendia.