But the timeline only diverged 22 years earlier, so that argument would only apply to people under 21 or so (allowing 9 months for gestation). More so for younger people, since the timelines would still be pretty close to start with and diverge gradually.
That'd concern whether these people would be in existence. But the question was whether they would be on the Enterprise
. Careers aren't decided by genetics...
Of course, with infinite alternate universes to choose from, we'd rather understandably get to watch the one where the same set of heroes is aboard. Plotwise, it would only be necessary for Guinan and Picard to be aboard, otherwise nobody would notice the need to send the E-C back in time and nobody would listen to the one who notices.
And the Klingon war in the alternate timeline started over a decade before the first Galaxy ships were launched, enough time that there should've been some major redesigns to gear the ship more for combat.
Would the redesigns affect the hull shape, though? Hulls seem sacrosanct in Trek: ships like Voyager
apparently won't move properly unless Kazon suicide boats or the holes left by them are patched up. Redesigning the exterior of a starship might be major work, quite possibly not worth doing for that extra 15% of combat agility or whatnot.