I mean, things are skewed not just because of the three teams we played, but because those teams, and several others, aren't even trying to win. So it was already pretty certain that the Phillies, especially post-Arrieta, were among MLB's 11th to 20th-best teams on Opening Day. Last year only 12 teams were even over .500, and all of the non-playoff teams in the AL were under .500.
If this rotation can perform like this in May and June they are serious wild card contenders for sure. If better competition catches up them, or some guys don't pan out (be it performance or injury), that 78-83 win target is still reasonable.