Too big ? - yes, definitely there is something "too big".
But then we are talking about windsurf size boards with low rocker - as they dont work at all and can not be ridden even if you wanted to
Only the smallest windsurf waveboards (without straps or straps moved forward) can be used for light wind if one wants (but boring).
SUP boards can be used too - also a size that CAN be ridden, but not much fun because you have to balance on the board, instead of using board control/steering to hold your balance.
If you are talking about surf board sizes, then the answer is NO, it can not be too big.
5'5 or 6 or 7 foot - they all work easy and great, if you just want to "kitesurf"
Although, for riding waves, it is a very different matter, and here size and width means EVERYTHING, and gets too big very fast !
So a wide 7 foot board wont work whatsoever IMO, if you want to ride waves (unless you are 150 kg)
But for kitesurfing, or riding in light wind - easy and no problem whatsoever with 7-8 feet boards