I think the main problem right now is the tyres - more specifically the poor modelling of their life cycle. At the moment, the rubber has only one and a half factors affecting it: heat and to a minor extent wear. With that I mean the only thing you have to watch out for is to not overheat the tyres and to change them before they pop due to wearing completely down.
You cannot ruin your tyres by overheating (you just lose time until they cool back down, then they're in perfect condition again) or overexerting them (no graining or tyre failure due to for example taking a curb in a bad way), you cannot flatspot them (technically you can, but even extreme flatspots have a minimal effect on performance) and the wear has no effect on the tyre whatsoever, other than making it cool down faster and weigh less, which means the more worn the tyre, the better. If anything, the wear should at least affect the relative camber of the tyre surface, making them work less well when the surface gets "equalized" to the ground.
Besides that, the R1 to R4 compounds are completely made up and not modelled after real tyres at all, and while that isn't necessarily a bad thing by itself, their current behaviour is limiting the compound choice pretty severely. It was a good step to alter the tyre heating behaviour and make the softest compound not automatically the one you'll choose for a race, but the general tyre strategy is still pretty much to take the softest compound you can get away with not overheating completely during the race.
The point is, tyres aren't modelled well enough yet to make the way you use them and the choice of compound realistic. Of course criticising is much easier than fixing, especially when things are done in the LFS way of modelling components and behaviours abstractly and just letting realism happen as you put the parts together.
LFS is at this point a brilliant simulator of vehicle dynamics, but when everything comes together it does not resemble the characteristics of real life racing all that accurately. I'm not sure if it ever will, either, but at least it has set a respectable landmark in sim racing.
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