I doubt argonaut will work that way. It seems to be developing in a similar fashion to "one for all" from "my hero academia".
Both start as special moves.
Both become more useable with a prolonged activity time (though it works differently in each case).
I imagine that argonaut may be matched to Bell's character growth.
As he was weak, argonaut became a special ability to give a normal boy the strength to become hero (it even seems to be a power stockpiling ability with intense recoil).
When Bell is growing, Argo Vesta and moving while charging were new abilities he unlocked.
I imagine the end of argonaut's evolution is less of a support style ability, and more of what one for all is, a constant minor application of energy slightly past Bell's normal means, granted with minor recoil, and potentially the ability to simultaneously release a super move after a certain amount of time charging.
That change would be good as Argonaut started as Bell being a boy wanting to be a hero, at the start.
He was a fool who acted as the xenos's hero during the arc when he gained the ability to move while charging.
In the wake of not wanting to resign himself to losing against challenges, Bell gained Argo Vesta, letting him step closer to being the hero he yearned for.
I imagine that the end development would be Bell being fully able to use Argonaut, being the boy who became the hero, not the boy who wanted to be the hero.
Note that all prior changes were indicative of Bell still wanting to be more than himself, be a hero, whereas the final change would be achieving the power to be a hero.
Or none of the above, and Omori will surprise us ;P
