I'm required by divine decree to disagree with your assertion that gallente sentinels are the best but I will admit that heavies have alot of fitting room. Then again, I have core upgrades at 5 and engineering and electronics at 4.

This is another way of saying "it's like fitting any other suit with max skills", tbh.

I've got PRO Amarr Sent (well, lvl4 and a few hundred 'Neo' ak.0 from a combination of faction packs and mauler events), PRO Amarr Assault, PRO Amarr Logistics and ADV Caldari Scout; if I had two points in FG Fitting Optimisation I could literally fit whatever I want without restrictions; as it is my IAFG takes up slightly too much PG for a second complex plate/repper.

vets are probably not the people to ask since we are likely to have cpu and pg skills maxed for a long while now. So even when we skill into a new suit our base pg and cpu will be far higher than new players who lack core skills.

Ironically I think CCP best bet, if taken in moderation, is to ensure low level suits have plenty of pg and cpu and then reduce it on higher tier suits on the assumption that players will have invested more into their core skills before using higher tier suits.

Saying that I believe if you have maxed out all the cpu/pg booster skills and all related skills that reduce fitting costs then you should be able to fit all proto.

Don't nerf the Proto CPU/PG
It's Prototype stuff. It should be able to fit anything.

Just do the same for Proto level on all Dropsuits classes.
For the price increase we suffer at Proto level, we should be able to throw whatever we want on it. Standard and Advanced modules on a PRO fitting is like fitting Yugo parts on a Ferrari.

We want to burn the ISK & Aurum.
Why is that so bad?

No, Prototype is not supposed to fit everything prototype, even with maxed skills.
You're supposed to pick and choose what you want to make strong and what you want to sacrifice.

Heavy obviously has too much CPU/PG, you literally CANNOT max it out.

I run all proto gear on my G1-S. I don't know if that calls for a Nerf but....You're correct I can not max it out. I'm foregoing the price tag of the Ferrari by putting all Ferrari parts on my Honda accord.