Yes, the most important factor is that TK's sims are coded by one man himself. Not only graphics engine, but also physics, AI, terrain, campaigns generator, everything. Big teams like MS Aces, Oleg's or ED usually consist of many coders responsible for their narrow part of sim development only.
Also please take note that with every patch new features are being added, some of them are very resources hungry when introduced (clouds, true self-casting shadows, etc.), but then in following patches performance increases, sometimes noticeable (vide stock WOI vs recent updates)
I'm running almost unmodded FE+EP1 right now, gameplay averages around 30-50 fps with more planes in the air than in most other sims (except BOB2 of course). Is this sufficient for enjoying it? For me, yes. Sufficient framerate is very subjective matter.