I think Sylar being a increasingly annoying turd that wouldn't flush was more the symptom of the relatively rapid creative collapse of Heroes
rather than the root cause.
Chiana from Farscape
was intended to die off but had staying power and Scorpius was also originally intended as a one off, but impressed the writers and fans too. Ditto to a similar extent for Seven and the EMH on VOY
Herrick was a fan favourite who nearly took over the UK version of Being Human
but unlike the inept creative team behind Heroes
keeping Sylar after his sell by date, the BH
writers sensibly killed off Herrick permanently after the first time he was brought back from the dead.