Yeah, 13th Age with only 10 levels is a bit more level sensitive, but on the flip side the monster charts by level make it simplicity to scale the numbers part of a foe up or down - I do it all the time when designing encounters.
Oh yes - I will actually just have the table of stats next to me and adjust stats on the fly. I've even reached the point where I can improvise a new monster in 13A by using the stats on the table and some ideas of how its attacks should work. The scaling by level system works well, and if I screw up and make things too hard the Escalation Die mechanic ends up covering a lot of design sins too I think it works even slicker than building creatures in 4e did tbh.
I keep trying to do something similar with 5e but the nature of encounter building in 5e makes it tougher to improvise monsters on the fly. I've been meaning to sit down and figure out how to get something that would work "well enough" but, eh, I have too many other projects...