Realistic Altitude or not?

Am I correct in thinking that even though the sim shows that I;m at 37000 ft that the sim isn’t really at that altitude? Whether I’m in an A320 or 747 the indicator shows I’m going up but the ground doesn’t seem to get any further than say 18 or 19000. Am I just not as knowlegable in determining altitude?

Can’t confirm. The difference between e.g. FL180 and 370 is pretty obvious.
IRL it’s impossible to even roughly estimate the altitude at FL300 or higher.