Almost daily I run into [rather, actively have to avoid running into] someone cruising at the same flight level as me.
Only one complaint with that, it just happens to be a significant one: if you’re headed in the opposite direction, there’s no reason you should be at the same flight level.
Here, again, we have people clamor for realism with liveries and which outfit flies where, but eschewing learning anything about actual flight.
So, here, for your learning pleasure, in both graphic and literary form, are the rules regarding proper flight levels depending on your [magnetic] heading:
As you can see, no one headed directly opposite you or me should ever be at the same flight level.
IFR aircraft [this means you if you’re in a commercial airliner above FL180] should be at odd flight levels for headings between 360 and 179; even flight levels for headings between 180 and 359.
It’s not arbitrary. It’s not your favorite flight level. It’s not the service ceiling [side note: the service ceiling is just that, you should not be flying at FL410 every flight, no matter the heading].
VFR aircraft [generally this for GA below FL180; VFR does not, as it is sometimes interpreted in IF just mean "Im in any plane I want but dont want RADAR controllers to tell me what to do; it means legitimate VFR] would add 500 feet to those altitudes (e.g. 6500 westbound or 7500 eastbound).
A note on bullet 3 on the link: Perhaps it’s best an actual pilot weigh in here, but it is my understanding that there is not much non-RVSM airspace remaining, with the advancement of instrumentation, etc. I think for our purposes, it’s fine to just presume that the rules for RVSM airspace are sufficient for IF. (Meaning every 2000 feet for cruising altitudes rather than every 4000. I.e. FL310, FL330, FL350…eastbound and FL300, FL320, FL340 westbound.)
With more and more people leaving their devices earlier and earlier, the least you can do before deserting your flight if you’re going to spend your time begging for realism™ is to set an appropriate cruising altitude so that I’m not flying eastbound at FL330 with some yokel coming westbound at me at the same flight level.
These prescriptions are in place for a reason. Flight levels aren’t arbitrary. And, again, FL410 is not the only acceptable flight level. That’s the service ceiling. Not the target for every flight regardless of heading.