Would "Sgt. Pepper's" be a better album if.....

Different Agoners would keep or cut different tunes.  There's no absolute answer, no consensus, on this.  If you put SFF and PL on this LP then what happens to the Magical Mystery Tour LP (without those two very strong tracks)? 
When I'm 64 is a fairly lightweight song (he wrote it when he was 16) but IMO they managed to make a good track of it.  And it is very popular.

Honestly, they would have been better off not doing MMT and gone on to the White Album.  MMT is the weakest album of their discography.  I'd almost say it was an album they released to satisfy the bean counters at Capitol, etc...

@sbs38
I think the 50th anniversary edition of Sgt. Pepper's that Giles Martin  produced was released earlier this year. Here are details, https://www.beatlesbible.com/2017/04/05/beatles-sgt-pepper-50th-anniversary-edition/

I believe you can stream Giles' version of Sgt. Pepper using TIDAL Look for the album artwork with the word 'DELUXE EDITION' on the left hand side. It's noticeably better sounding than any other Redbook CD versions I've heard and miles ahead of the mono CD version that sounds lifeless.

 With all due respect to the hypothetical question you posit here,  with my full disclosure that my intention is by no means to denigrate let me ask the rhetorical question if I may:  given that Sergeant Pepper is largely regarded by most all legitimate rock 'n' roll historians and critics as the greatest album of all time and largely "perfect,"  why would anyone even attempt to suggest that one could improve on perfection and or the greatest albums of all time? Why not let "sleeping beauties" lie and appreciate what you've got? :-) 

saintintn, I think MMT is far stronger than Beatles For Sale, which is such a disappointment coming after the very strong A Hard Day's Night album.  I do agree with George Martin that "the White Album" should have been a single disc and not two.  That's the one (of the later ones) with a lot of filler.