Now I know there have already been lengthy discussions about this subject in every medium where DnD is discussed. The simple fact of the matter is, Casters can make great martials, or replicate most martial abilities, but can also do a plethora of other things martials can't do (unless martials play a subclass/take feats that let them just pick which limited section of caster power they want).

I feel like the most obvious and fun solution to the martial/caster divide is just giving martials abilities that offer similar power or utility for casters, with the same room for shenanigans and flexibility, on similar levels. Hell, not every subclass needs as many options as casters have spells, so probably most of these abilities should be stronger than spells casters would get at similar levels. I am curious what the argument against such game design is, as I assume it has already been discussed before.

It is crucial that these abilities aren't just spells that are reflavored with the same resource cost (or just straight up left the same as is the case with Totem Warriors), because 1 - a caster can always just choose to get these spells as well and 2 - you then have to balance these spells with the casters in mind as well.

A lower level example of this would be letting Barbarian's get an ability similar to earth tremor (a first level spell that isn't even that great), but improved if it costs resources or just made resource free, which they can do by slamming their weapon onto the ground, or maybe even just as a part of going into rage. You can extend on this by letting them slam their weapon not onto the ground below them but onto the ground in front of them to create concentrated difficult terrain. Balance this ability, and it's progression, in relation to spells casters get around similar levels, like web, plant growth, black tentacles (however, again, improved in a way that reflects the class, as casters simply have these as options).

I'm not talking about damage (although as someone who loves Monks letting them use a non-concentration haste without the lethargy affect after 3 rounds for 3-4 ki would be amazing), just more options instead of damage, more stuff to think about for martials, in a way that fits their core fantasies. You can give Drunken Master monks, who gain proficiency in brewers tools and performance, an action they can do that inflicts a charm/poison condition on a number of enemies, fitting in with the core idea of the subclass.

I'm aware I'm still mentioning spells for reference, but I think starting to think of these abilities without reference to spells in conception is ideal. Aside from an argument against such game design, I'm also very interested in what people have as ideas for such abilities.

Edit: Core part of this I forgot to mention is, you'd want these abilities to scale similar to casters who can literally change reality at higher levels. Barbarian's moving mountains, Monks getting something equivalent to time stop at the same levels etc.