We can just make a list of games that ARE D&D and see how divergent they get. Obviously we have all the games with D&D on the vocer and in the name, but we also have:
Pathfinder 1E
Shadowdark
OSE and other reetroclones
and arguably Pathfinder 2E (not remastered) and maybe 13th Age.
There are a TON of games that aren't D&D but are inspired by it, from Stars Without Number to DCC.
What are the things that are common throughout all of those? Off the top of my head: the 6 ability scores, hit points, classes, levels. I don't know if they all have saving throws or AC.
This strongly suggests that no, not having ability scores, is probably not-D&D. Which is too bad but hey, them's the breaks.