Ok so i think TLR and all Fullborns arent as powerful or as strong as everyone believes them to be. Why? For two primary factors.
The number of metalmimds they can have on or in their body is limited. On top of this the size and thus the storage capacity of their metalminds are limited.
While they can compound their abilities for more power this literally destroys their metalminds to do so meaning they can and will run out. Especially if they increase how much they tap from the metal.
Fullborns have the potential to be the strongest but realistically they aren't. They have upper limits to their powers and can't infinitely amass power. Imagine needing to carry 16 different metal implants inside your body. If your arm gets blown off or cut off you lose those metal minds, you can't have all of them attached to your ribcage/torso and even if you did they'd be too small to realistically last long enough or store enough attributes.
They are powerful dont get me wrong, but they are not as godlike as everyone says. Even with Steel Compounder Speed they have to tap or burn other metals just to survive those insane speeds and you get a few good bursts of speed before you use up all you got.
I'm probably gonna be held at gunpoint for this opinion but I'm tired of pretending I'm wrong! /j
Also as a final note, The Lord Ruler knew about all 16 metals but did not have access to all of them. Meaning in a normal fight, not using hypotheticals or what ifs, he doesn't get like 4-5 of the stronger metals. That's his fault for screwing over technological progress.