It's likely the cars are just generally being under built for the amount of power they can put down now...
Like in electric, you don't really want to have a big bingle in electric, but where the saving feature comes in there, is the bulk of people only strapping in a 21.5 or 17.5 turn, and lets be honest, your then just not going fast enough to 'really' wreck something.
Strap in mod like power though, and they just about break something standing still...
I think nitro is a little the same, or becoming simular, so much power and speed, less mass to the cars, and in nitro your always going fast, or faster than other things.
But it's likely why they are trying to slow down 8th scale, reduced wings I think, smaller carb restrictor, and there was something about reduced nitro in the fuel.
Someone else said it, but quite likely is they are looking to tame down 200mm next, I'm not sure at all if any of that is good, still not been in it long enough to judge that, but I will say, as someone who does 200mm now, if they do bring in the restrictors and reduce nitro in 8th, I'd be bloody tempted to jump to 8th scale, no kidding there.
As to fragile nature of lighter cars?, well so far I'm not seeing it, I have seen those Caps hit walls at speed and break nothing, and so far I think my MTX5 is as tough as the G4JS or CD3 I started with, even compared to the 4 I'm not sure it's 'that' much more fragile...
Old Jedi master Trev (can't see the cars at night so drives using the force...) seems to think the strength peaked at the 3 anyway, but in the hands of newbies the 4's seem to hold up quite well, but 'overall' I'm just not sure any car and it's breakages relate to things how we think they do, I think in the end people and newbies in general are more happier with just a better grade of car?.