Here is some ideas on lighter models
1 - I don't use any carbon fiber except fo once -on the Petrel-
no other carbon till I get to the lil electrics - then I use it .
I do evaluate every last part of the model tho - and you can't believe how much overbuilt stuff exists in kits -especially ARFS.
remember - the plane does not have to stronger than the weakest piece in it -
for example - the entire bare airframe for my old Buckers - weighed 6 lbs - 1800 squares - all up weight 16.9-(Tartan twin )-to almost 18 lbs (ZDZ80 single) -and there has never been any problem with strength.
The airframe is where you really save the weight - then put in only the pieces needed - no " beef it up" stuff .
On many of my models there is no engine mounting plate - just angle struts that attach engine to longerons .
It works for full scale ---