See, I am also a long-time fan, but I had and have no patience with all that y-e-a-r-r-r-r-r-r-ning Chapel did. It's just so weak and poor-little-woman-ish. I know that's partly because it was filmed in the 1960s, and that was typical of the time, but now? No. Or at least it shouldn't be. Yes, I know that even now in the 21st century, people still yearn after those they want but cannot have, and people presumably will in the 23rd century, too. But when it's a woman yearning after The Unapproachable Male, it's almost always dull and hackneyed. At least IMO.
So they needed to do something different - and why not Uhura? I admit it jolted me, not because of race but because it was Spock! and Uhura! SpockandUhura! UhuraandSpock! But who says a jolt is a bad thing? Not me, at least not in this case.
If they'd made it Chapel, it I would have hoped to God that we would have had something besides y-e-a-r-r-r-r-r-r-ning.
As for the question of Spock having a relationship at all, I was against it at first, but that was until I realized that we are simply talking about a series of movies here. I mean, I might have found it tedious in a TV show (mostly because most TV, and that includes Trek, is not good at showing long-term romances, and I lose patience with all that break-up-get-back-together stuff that TV is addicted to), but in a movie...it might work very well. It did in this one, for example, although I'm hoping in the next one we get to see more of Uhura as an officer rather than as a love-interest.