Solved

KERS has no effect with DRS

Is this meant to actually be a thing?

Cars have a limited top speed.
Maxed out DRS allows the cars to reach that top speed.
Only low level Technology cars get any benefit from using the two at once. Otherwise you are only wasting the boost.

Well then, can't wait to be level 20 to get that kind of speed from DRS haha

The difference in DRS is just shocking some cars don't even close the gap to the car ahead with DRS on it's own.
With great knowledge of it now, they should maybe Edit it slightly & have only 3-4 versions of DRS