No. In any case without Reagan, it's a closer election. Poppy Bush is no Reagan, Anderson is no Reagan, Baker is no Reagan, Connally is no Reagan, Dole is no Reagan; hell, Ford is no Reagan. But any of them would've still killed Carter in 1980. It was just a Republican year.
No.
Lower, or in some cases, even losing again.
No. Carter was the wrong man in the wrong place at the wrong time for 1980, & again, anybody would've still killed him in 1980. It was just that Republican of a year.
Can't underestimate the power of incumbency though, and there's still the reasonable grip on The South that even Reagan had some time getting through, along with the natural hold on The Northeast.
While I have little doubts about where the popular vote would go, whether it would be enough to beat the Electoral College advantage Carter had is another story. I mean, would Dole have been able to crack The South? Would Connally or Baker been able to flip The Northeast and Midwest? Where would Reagan have ended up if Anderson hadn't eaten away in The Northeast/Wisconsin/Illinois?