Never watched Heroes, but Lost had a pretty noname cast aside from the one hobbit and maybe the guy who played Linus. OK, also Michelle Rodriguez of course but she didn't last on the show a long time if I remember correctly? And Daniel Dae Kim had a bunch of roles before it but they were all side characters.

Most of the main cast that had to be there nearly every day of shooting consisted of folks who didn't have to put off other major roles to do it.

And it was a season a year, wdym only a few months between seasons?