Suggested

Engine Modes and no Refuelling

Yes, the option for a refuel ban would open up a whole new race experience and strategies. I don't think it'd be the better option but sometimes just doing something different in a while is a great thing in itself.

Engine modes is mostly mixture settings. Broadly speaking, on the rich side of the spectrum, leaner means usually more power and less consumption, but running hotter and higher risk of engine knocking. If you go richer you loose a little bit of power, have higher consumption but the engine runs cooler (as the additional vaporising fuel binds heat energy) and reduces knocking, which for using the same octane rated fuel means you could use higher compression or turbo pressure giving more power (but also even more consumption).

A really old game, Ferrari Formula One, from the 1986 turbo area, no refueling and max fuel limit regulation (192 litres?), did that part pretty well. Pre race you could set your fuel amount and ECU mixture, during the race you could adjust the turbo blow-off valve and thus pressure and power, on the fly. Setting lean ECU meant you could theoretically use more average turbo pressure without running out of fuel as the base consumption is lower, but lean ECU also already meant higher engine wear and risk to blow the engine by running it too hot on long full throttle tracks, too much average turbo power too long or simply going too high with turbo pressure (knocking). Rich mixture meant higher consumption at slightly less base power but you could use more turbo (and thus a lot more power effectively) more safely, but again in theory, as that large fuel display often showed pretty soon you're in trouble going on doing that. So you had to find the best compromise in ECU and in race dial your turbo setting both wisely and tactically sound.

I was just trying to explain, without going into the depths as with fuel injection you can do quite a lot more things breaking that generalisation above. I'm not saying the game needs it. I'd welcome it but I'm hardcore in those things, the more to fiddle and tweak the better, but this game has to provide a balance between play styles and to be able to do a race per day, so I understand to keep it simple (on the outside, as going into the races it's nicely complex and there's no end to figuring things out). If I feel the need to fiddle in details with engine parameters I can still play Automation. ;-)

Also, at least until everything settles, the tyres offer choice. 3 stop Soft wearing to 40%, 2 stop Soft going down to 30% but can afford to loose 20 seconds in lap times or Mediums that almost manage to stay above 50%, or even 1 stop Hard as they can loose 20 and 40 seconds in lap times to still be the faster option. Then there's mixing compounds.

Of course in time people will settle into single dominant strategies, but that's often no different now with refueling, so that no refuel option allows at least 2 different races per track.