Well, they're both fictional lyricists in that neither of them is setting documentary texts to music, they are both making up their lyrics. So the simple answr is no, you can't say that about them.
If you mean are Lennon's more grounded in reality - no - when Lennon gets political he tends to operate in some fanciful utopia rather than any real politics (cf the pie in the sky nonsense that is Imagine and Revolution or the soppy romanticism of Woman). McCartney often does frivolous lyrics as well (Frog Chorus, Pipes Of Peace, O-Bla-Di-O-Bla-Da) but his tend to be deliberately chidlish or childlike, whereas Lennon's seem to be intended seriously even though they are just as daft.