It all comes down to whether you believe ( and it has to be "believe," because there's no other way to put it) Rose's "presence" somehow offset his lousy performance in 1980. Pete Rose played all 162 games for the Phillies in 1980, at first base - and turned in an OPS+ of 94. That's 6% worse than an average offensive player in that season - from our first baseman. (Rico Brogna actually did better than that in 1998 and 1999 - think about that.)
I don't buy the idea that Rose's "presence" somehow made the difference between what happened in 1978 and what happened in 1980. Danny Ozark made a bad mistake in 1978, in a critical game, that cost the Phillies dearly. That wasn't a function of the "absence" of Pete Rose. But beyond that, the Phils' post-season success in the run from 1976 through 1983 was about what one would expect. Five division titles; two pennants; one WS win. That's dead on with statistical probability.
Here's something else (not entirely serious, but maybe it makes a point) to chew on. The Phils got to the World Series in 1980 and 1983, after failing in 1976-79. They added three players in 1980, who were still on the team in 1983. Perhaps those three players were the "difference," instead of Rose (who came aboard in 1979, and "led" the club to a 4th place finish that year). Those three players? Luis Aguayo, Bob Dernier, Ozzie Virgil. QED.