You cannot be sure that Merc would have 3 stopped minus a SC. If anything, I have heard Toto repeatedly mention that all they need to do is mirror their opponents and they have put it to good effect over the last year. Vettel definitely seemed more at ease with his tyres than the Mercs but minus a SC, he wont be running in clean air and a car ahead was maybe all that was needed to negate their slight tyre advantage and force Vettel to stop as many times as the Mercs did.
that's awesome that Toto said that, however they couldn't make the tyres last long enough for a 2 stop. Hamilton was running out of tyre on the primes in under 20 laps and the options in 12