R3d,
Actually when engine capacity was 10cc there were no 2M or 11lb planes, they were typically around 65" wingspan and 7-8lb.
The unrestricted engine capacity rules (to allow use of cheaper engines !!) drove the size and weight increase of planes to the 2M & 11 lb limit !!
Increasing the 5kg limit would IMO escalate the cost once again, as I said previously.
Now,for all but the highest class you don’t need a full 2M plane. The Sebart MythoS 125 is a great example (there are others) - almost 2M size at 1.9M and 1/3 the cost of the MythoS Pro, flies great on 8S with either a Hacker or Motrofly
$200 motor. I’ve seen this model also do very well on 10S with low cost motors.
Steve