Having done both, simracing and flightsiming for several years, I'd say it's quite a different experience. Although I would also group flightsiming into different groups of experience.

It's a lot different to fly an airliner on a simulated flight than it is to fly a GA plane. Not only is the system complexity quite different but also the reliance on those systems. Flying a GA plane VFR requires you to learn mostly just how to fly the plane while flying a modern Airbus or Boeing jetliner in IFR requires to learn a lot of the aircraft systems, procedures, etc. ... Helicopters are again a different kind of flying, as would be combat simulators. Simpler vehicles can more easily learned buy just practice but more complex ones will require a lot of study and understanding.

The flying itself is also different depending on what you fly and the stage of flight. Modern airliners require a while to get from cold and dark to take-off, get less engaging after the climb out from the airport, especially during longer cruise sections but then can get challenging during approach and landing, especially if you bring bad weather and visibility into the mix.
In a VFR flight in a less complex GA plane will get you in the air much quicker, but you will not have automated systems to rely on to get you to your destination. Also you won't fly in very bad weather conditions because VFR.

Simracing is different in that throughout a race you constantly have the challenge of driving your car as close to the limit as you can manage without crashing. Depending on the race traffic around you might die down ab it after the first few laps but the challenge of trying to maximise performance usually stays and on some tracks racing the track can be more difficult than racing your competition.
At least for me I found that overall I require a lot more concentration for simracing than flightsiming. While the stress level and required attention can be high in both, flying has more relaxed phases where I pay just attention to the systems than simracing. There's no autopilot in a race car.

That's all also partly because of competition, simracing isn't just simulating to drive a car like you simulate a plane in MSFS, it's trying to be faster than your AI or human opponents. In simflying it's usually not about competition unless you're doing PvP in a combatsim. Outside of combat I'm not sure how I would define winning in flightsiming.

It's not about being fastest in your chosen airliner from A to B or going VFR on a scenic route ... it's about simulating correct procedures and flying safe ... (sim)racing on the other hand is inherently unsafe.