Good ESCs have lower resistance in their FETs (transistors).
Resistance makes the FET heat up when passing current.
An ESC has a "motor rating" worked out by max current it can
carry before the FETs heats up too much.
Better (more expensive) FETs or just using more FETs (in parallel)
gives lower overall resistance... that is why ESCs rated at
"no limit" cost more than something with "20t limit".
The expensive one will have lower resistance & low turn rating.
So passing current through a cheaper ESC is like pushing water
through a tiny hosepipe... water does gets through, but slowly.
When there is "no limit", its like using a big fat fire hose!!
Even if you're only running a stock motor, a better ESC will always
outperform a cheaper ESC as it can carry more current faster.
A lousier ESC starves the motor as well as wasting battery
energy by getting its FETs hot.