That something is expensive has no bearing on quality. E.g. here in France you can buy plugs and outlets ranging from good quality brand names ones (usually Legrand and similar) to utter disasters that are unusable, break at the smallest provocation and are an electrocution/fire hazard in the worst case. And all bear the state certification logo! The price difference is often fairly minimal.
The failed socket you had was poorly made and the pin was either not welded in properly or the weld has failed. Thickness of the outlet plastic has no bearing on it because the ground pin is always supported from behind.
I am from a country that has these outlets with a grounding pin sticking out, here in France these are the rule as well and have never in my life (40 something years) encountered a socket where you could push the pin in while inserting the plug.
If the plug isn't going in properly then either something is deformed or, much more common on recent sockets, the stupid protective shutters in the holes of the outlet don't want to open. I am routinely taking this BS out. If the shutters are in place it can literally take serious pounding and wiggling to insert a plug, even on good quality outlets. If that's the case, do yourself a favor, open the socket and take this nonsense out. You will thank me later. It is only a sliding piece of plastic and a spring.
If someone is worried about kids, there are lockable plastic plugs that can be inserted into the outlets available, preventing a curious kid from messing with an outlet.
See e.g. here:
http://abc-electronique.com/annuaire/montages/cache/1457/muliprise2.jpgThis is a typical, bottom of the barrel, cheap piece of crap extension cord available here. See how is the ground pin welded/riveted to the busbar at the top? And that bar is supported from behind by the other half of the case. Those pins aren't going anywhere, even on this piece of junk.
The photo also shows the protective shutters - the diagonal plastic things with the green covers under the live and neutral bus bars.
Or this one (combo with a switch on the left):
http://leslogesdeserrigny.fr/wp-content/uploads/2019/01/brancher-prise-electrique-avec-sch-ma-lectrique-pour-branchement-interrupteur-prise-idees-et-inter21313425394-avec-brancher-prise-electrique.jpgSee the metal earthing strip? That's what is holding the earth pin. The plastic has no role in it. If you have managed to break the pin off from that thick brass strip, that's not normal.