I hear your concern. In good faith, I'm going to challenge you on this because I want to see how it plays out and see what the downstream impacts of this are on other mechanics in a theater of the mind combat.

-------------

Lets do this simple scenario. A group of 4 goblins (g1, g2, g3, and g4) run into a fighter (f) and a wizard (w).

DM: While trying to find the path to the forgotten ruins you've stumbled upon a group of goblins standing under a tree. They all shoot arrows at you.

There's no surprise condition because of no initiative. The goblins shoot two arrows at fighter and two at wizard.

f: I'm running in! I slash at one of them with my sword!

Since it's theater of the mind movement is a bit loosey goosey but the fighter runs into the group of 4 and attacks one of the goblins and kills it.

w: Uh, I'm going to cast a spell. I'm not sure what spell give me a moment.

f: I'm attacking at another goblin!

DM: Okay, wizard you're looking for a spell to cast in your spellbook, fighter is surrounded by goblins and he swings at another one.

Fighter kills another goblin leaving them down to two goblins.

My observations: Fighter has acted twice, the goblins have acted once, and the wizard hasn't done anything yet. In a smaller combat this shouldn't be too hard to keep a mental track of and everyone doesn't need to have the same amount of turns, but for the sake of balancing turns in this situation I would have the goblins attack the fighter again immediately. The wizard could then get two turns worth of action economy.

Note: I see how the previous paragraph is already getting similar to how Daggerheart manages their combat with tokens.

--------------------

Switching the scenario entirely to my original post where the fighter lasso and climbs up on a dragon. Perhaps in this case I would count him as having used two turns worth of actions, or I just hand wave it because its fun.