The WC1 'sim wasn't endless -- you had four waves of each fighter, depending on where you started. (1 Salthi -> 2 Salthi -> 3 Salthi -> 4 Salthi -> 1 Dralthi -> 2 Dralthi... until you got to 4 Gratha. If you beat 4 Gratha, you won!)
The WC3 'sim is more than just the Flash mission -- there are ten or so training missions that introduce you to the basics of the game... you can use them at any time during WC3 (while on the Victory, at least). The console versions (3DO & PSX) had different sim missions.