Either you aim for realism, or you don't. LFS aims for realism, real cars stall, LFS cars should stall, there's no way around that.
Real cars with normal gearboxes get transmission / motor damage when you don't cut the throttle when shifting gears, so LFS cars should, too.
In real cars you have to unclutch
before you shift, should be the same in LFS too, doing otherwise demeans the skills demanded for adequate gear shifting, and disadvantages people who drive more realistically.
It should also be said that with proper knowledge of the gear ratios, shifting without the clutch should be possible, like in real cars too, with the right throttle control, of course, allowing for faster gear changes, with of course nasty consequences like a missed gear and therefore lost time / damaged transmission when not done properly.
The clutch is one of the reasons I love LFS so much, why not add some more ?