Greenwood made 4 appearances, not 2. He played 42 minutes less than Obi overall. That is not significant.
I'm not even bothered about comparisons between the two. Totally different players, different physiques, skill sets, development, style of play coming through years apart in teams that are completely different.
I'm just correcting your factually incorrect assertions that Obi has had numerous starts (he hasn't) and played considerably more than Greenwood did in their first seasons (he didn't). I'm interested in peoples different opinions on Obi's potential and future development, including yours, but theres no need to twist facts in order to justify your point. You may have a good point that can stand on its own merit.
My 2 cents is they both played a small number of minutes, and both looked like they weren't yet ready for adult football, which is completely expected for 99.99% of 17 year olds. There is no significant conclusions to be drawn about Obi from their first 100 or so minutes of adult football, just as there wasn't any significant conclusions to be made from Greenwood's first 100 or so minutes. But from youth football, it was clear Greenwood was a top tier talent. Obi is a beastly goalscorer but much more one dimensional and stands out at youth level because of his physique. It's yet to be seen if he can transfer that into the adult game and, if so, at what level. There's a demand at every level for a physically dominant striker who can score bag loads of goals, so his skill set is desirable. That type of striker generally makes an impact in adult football a bit later than nimble dribblers/wide forward types.