An improved defense should have a big impact on the pitching staff, especially young pitchers - remember, this was an historically bad defense, and that has a psychological impact (as well as physical, extra pitches and more stress) on a pitcher, you make a great pitch, your defense doesn't finish the inning, it's natural to lose focus, especially for more inexperienced pitchers.
As far as hitting, they had some black holes in the lineup last year, just replacing Kingery/Crawford at one spot helps (and if Kingery becomes the hitter he should be, a much stronger bench).
Last year they cycled through a bunch of young pitchers and moved on, Lively, Thompson, Garcia, Leiter, and gave up on Kilome - but they have more than enough replacements - the thing with young pitching is always quantity, top guys get hurt, second tier guys change a grip or release point and surprise. In the past, we'd pray that the one or two pitching prospects would come through, now there's a new group every season.
The real key is going to be the new hitting instruction in the minors, they have to do a better job of developing young hitters - too many under perform. You're not going to suddenly turn everyone into a star, but how often do young hitters in the Philly organization surprise v disappoint? I do think there's been a shift toward more disciplined LA hitters the least few years by the scouts, now it's a matter of taking one or two up a notch.
To me, FAs are the icing, but if you screw up the cake, it's hard to put the icing on.
Phillies have to improve their cake baking skills before we should get overexcited about FAs, build a good solid team and FAs will find this a more attractive destination, use FAs to build a team and you'll always be chasing your tail. Angels are a good example.