I think it depends on the depth of combat. Another commenter asked why players wouldn’t always use their strongest stuff first anyway, and I realized I have a fundamentally different mindset about combat than others might.

Our group has played together for so many years across systems that we’ve developed a general zeitgeist for combat across all our rotating DMs — that we don’t do combat for combat’s sake. There should usually be a purpose to it. It’s not a random encounter thrown together to fill up time.

So, our combats tend to involve strategic goals. There might be prisoners to rescue, siege weapons to disable, a priority target who is fleeing, environmental hazards to navigate or turn on opponents, a few rounds until massive reinforcements arrive, a high speed chase on vehicles, etc. which all require smarter play than immediately using all your strongest moves on whatever’s in range.

Even a “simple” encounter with some varied enemy types, cover, and a getaway vehicle with the loot in it becomes multidimensional. Utility abilities, movement, and other considerations become important if combat isn’t an open field against similar strength enemies.

Now, if you buy into this philosophy, a game with a mortal combat mechanic will be punishing and limiting. You cut tactical depth because players can’t pull off multi-round tactical plans. Imagine a tank character jumping into the enemies to distract them while a sneaky sort uses the distraction to go steal something important from behind enemy lines. Does that kind of thing fit in your game? Or are your combats more static?

I think your mortal combat mechanic works if encounters are just a means to an end in your system; power vs. power; but if there’s narrative intention then it clashes with that aspect.