They have the same amount of HP than any other line infantry, so tell me how could they be less durable. Allied wiping potential have been constantly erased in the last patches, today you really need to be lucky, or to have bad luck, to get your gren squad wiped with a single shot.
4 man squads have 320hp. 6 man squads have 480hp.
Given that you need to retreat with about 80hp left (2 half health models) so the squad isn't wiped, Gren squads have to retreat after taking 240 damage, while the similarly priced con squad can take about 400 damage.
Cons do have a target size of 1.087 I think, but that's not even 10% increased RA in exchange for 50% more health.
Grens have great damage output but have the worst survivability amongst mainline squads - pretty much everyone who plays this game regularly can agree on that.