When the discussion is SPECIFICALLY about range then yes someone with only one title can be in the discussion.
Range is a meaningless concept unless it actually leads to winning something. It's only "to make some people feel better for not winning more." Whoop de do. Let's make a special medal just for that.
Kipchoge does win a lot. He's won a lot of marathons, but not the big race yet. If he does not win in Rio, then his London win loses a lot of it's meaning. A great result, but maybe he should have concentrated on the most important race rather than peaking too early.
If he wins, then it's great and his range has lead him to be the best current marathoner. All his other wins and great times serve to prove he's the best. There will be no real debate that for these past 2-3 years he's the best. If he loses, the debates will never stop.
There are always those people who concentrate moe on great times or the number of great races, but the point of running is to run the best at the most important day. I'd much rather be Frank Shorter than Bill Rogers. Rogers ran better (marathon) times, and he won more majors, but Gold and Silver (or Gold again if you discount cheats) is far better.
Heck, I'd rather be Billy Mills than Ron Clarke. One great, amazing race at just the right time over years of dominance and world records, but that's me. I know a lot would disagree.