No Lokihel, if you are powered the same when riding on your board, and same kitesize, the current doesnt matter at all, relaunch is precisely the same no matter how much current
To compensate for current, we choose a bigger kite if downwind current, and a smaller if upwind current - to get the "right" power when riding, of course, to be powered the same when riding, this is something you learn but takes a lot of time and you can still be surprised sometimes.
Meaning, that if a bigger kite in general is harder to relaunch, there is a difference, agree - but if same kitesize and powered the same (two different scenarios), definetly no difference no matter how much current.
In really strong downwind current, we often choose a bigger kite than would be sweetspot when riding, so we can go upwind better, a tad overpowered so to speak - at least at wavespots.
But this is not the topic here...
For bodydrag yes, it is assumed you are in approximately the same current, but this is almost always the case, for most kitesurfers at least, with very few exceptions only
Peter