I think, jumping in here, it may be good to reinforce the challenging of the assumption that martials should not have a daily resource pool, and to ask a simple question:
What are the actual game design problems with Vancian-styled casting (by which I mean both proper Vancian casters and other slot-based casters like spontaneous casters)? Yes, "feeling bad" is a valid design critique to an extent, but Vancian style does not feel bad to everyone, and is certainly not the cause of the actual problem being discussed (see 5e and Pf1e where casters use the same system and are gods among men).
Beyond that, operating with the assumption of keeping spell slots, I would like to introduce my own idea:
Universal martial resource points, and a resting system. Under this, every martial would get a pool of points that they can use to create more powerful effects. As a general rule, both martials and casters should be able to function without their resources or with low resources, but it should be expected that you will use them in most non-trivial encounters. So not using them or having a very low amount would increase the severity of the encounter by one. A moderate encounter would become severe, a severe encounter would be extreme, an extreme encounter would be basically a suicide mission, etc.
As I stressed, you should be able to do most things without using them, but you should be expected to use an average of about 1/turn. This assures that a class doesn't need to just stop functioning after a while, but attrition will still be a thing. Your Barbarian doesn't stop being a Barbarian once you're out of points, you can still rage, get whatever powers you get while raging, be a Barbarian, but you won't be able to hit that guy really really hard, only normal hard.
On top of that, to give the players a way to actively combat attrition, you allow them to rest without ending the day. Mechanically, this just takes a bit of time and restores some percentage of a martial's point pool and 1 slot per rank for casters. And most importantly, is 1/per day, mostly to prevent the opposite problem. This lets players who are really good at resource management have their cake by generally letting them maintain higher resources than a player who is bad at it, while avoiding shutting the player who is bad at resource management out of the fun parts of their class.
Finally, you would greatly expand the concept of cantrips. You should be thinking of cantrips like a caster's equivalent of a basic Strike action, not a backup option. If you want casters to primarily be buff/debuff/control as their role, then they need to be able to do that all the time, just like a martial can always Strike. Give them cantrips that let them apply minor buffs and debuffs and control effects, on top of ones that deal damage. Give them more interesting spellshape options that can be applied to cantrips so they don't get locked into spamming a single simple cantrip.
