[javawizard]

Jet engines do not strike me as being inherently simpler than muscles, not by a long shot.

They're still the best way we know of going about the business of building a flying machine, for various reasons.

[rightbyte]

Piston engines surely are more complex than jet engines though? Which replaced the "flapping engines".

[readmodifywrite]

They are not. Turbine engines require much higher quality manufacturing and tolerances and operate at much higher speeds and pressures. There is more to it than the perceived number of moving parts.