Plastic Ono and Imagine were amazing records. My opinion, however, is that George had more classic songs on his first than either of those two. Now if John had done a double album to debut i would probably feel differently.
A Beatles scholar I used to listen to said that George coming out with the debut double album was a FUCK YOU to John and Paul
I don't think George ever attained the songwriting prowess of John or Paul. That said, he had built up a surplus great material in 1969/70 which couldn't fit on Let it Be or Abbey Road based on his normal 2 songs per LP quota.
I've long said, it you take the 13- 14 best songs off each of their solo debuts, you might have the best Beatles LP ever.
Instant Karma
Mother
My Sweet Lord
Isn't it a Pitty
What is Life?
Maybe I'm Amazed
That album would have been YUGE.