On certain cars that's certainly true, but there are definitely some cars that benefit a lot from even just 10 minutes of adjusting the suspension and downforce. My experience with the 911 GT3 (996) on daily race B was that the stock settings were already very good and that any attempts by me as a beginner to try and change the behaviour weren't resulting in any consistent lap time improvements.
On the A110 '17 though the stock setup wasn't anywhere near as 'race-ready' and I've been able to shave off two seconds off a lap with my own suspension setup. It's still an ongoing project though and after driving the 911 my eyes have been opened a bit to what kind of on track behaviour I should probably be building towards. I'm still almost a second quicker with the Porsche than I am in the Alpine right now, but more importantly it's much less effort to be fast in the Porsche.
But you know what, I think that's pretty great! It seems to me that some people are complaining that because there's no BOP, you can't use certain cars at stock settings because they're not competitive with other cars which are better at stock, like the 911s. But let's be real, on GTS with BOP there have always been cars that aren't competitive.
If you don't want to tune, then don't use the cars which require tuning, use the cars that are competitive with their stock setup. The rest of us can sink hours into trying to get other cars to be competitive.