Don't blame the aircraft for being stuffy and claustrophobic in the back; blame the kit you have to wear. In countries were the sea is always above 25 degrees tee shirts and trainers are the rig and there are no complaints.
As the suits and rebreathers are compulsory then the room for them must be allowed for. Passenger weight has been progressively increased over the years from 170 lbs so now is the time to allow for the extra bulk and increase the seat pitch.
Should passengers numbers be reduced then so be it.
There's a reason we wear re-breathers and survival suits. People (including pilots) paid with their lives to discover it.
Even with shorts and t-shirts on it's going to be stuffy and claustrophobic unless you have 19 vertically challenged PAX in the back. Most people of average stature have to almost bend double to get out the back. Try it.
A poster earlier in the thread alluded to the fact that one of the original design criteria for the SP was that it could be carried by rail ie. it was designed to be cramped.
I've only flown on an EC225 once (I crew change on an S92) it was a very empty flight, still a bit cramped headroom wise but the seat layout was a little better and the large push out windows soothed the fears of my "inner chimp" to paraphrase another earlier poster.