I tested some of them to check temps too, all were hotter than mine, specially within the most populated Apple Store in Barcelona, with the new MBP's located at the top floor were by difference the hottest ones (heat rises) ... so ambient temp is the most determinant part of any cooling solution, since the curve that elements take with higher ambient tends to be exponential rather than lineal.
Second part, definitely, if you're using it for hours, total package is gonna become hotter and is not going to go down, specially with the default fan curves, when I showed you the first pic, Mac was lit-on just for 40 minutes, now 1h 30 min has passed in total, doing the same activity, temps have rised 2ÂşC and ambient just 0.5ÂşC more, here's the last screenshot:
View attachment 1943144
And no, you're totally right, your electronic devices can get hot and will remain to work, but here's why, in some circumstances if the temperatures are really high, normal behaviour for the CPU/GPU is to throttle to avoid to burn those components and others responsible for its correct operation such as voltage regulators for example, worst case scenario to avoid bigger damages, it can shut down by itself (my iPhone once did on a hot summer beach day) to prevent a disaster. Not to mention, that if the components are always running hot and/or in the limit, you're shortening its lifespan and surrounding elements such as the battery.
I'm saying this cause you game on your MBP as you specified, so you want to get all the juice out of it for the longest period possible, my advice, keep it fresh and adjust your fan curves to avoid any issues, even if you want to let your hard case on, which I find totally understandable.
edit: I don't know the exact data, but from what I've seen and read, 95-100ÂşC can be a perfect threshold on which these MBPs can start to throttle down the speed; and btw, despite all of my "running cool" MBP, the other day when I played Dirt 4 (it's supported via Rosetta) 1080p @ default high settings, whole package was on mid 70's, sometimes peaking nearly 80ÂşC, and neither was stretching the CPU more than 50-60%, automatic fan curve made the mac to last 10 min fanless in the 75ÂşC range and just then, made them spin at 2500 rpm (Apple prefers quiet computers rather than extreme cool ones) so I think these machines can sustain perfectly 80-85ÂşC for some hours without any compromise, and if you tune the fan curve, they will run fresher.