I have recently managed to buy perhaps the last ever reasonably-priced copy of JC Powys's last worthwhile (albeit crazy - but that goes without saying) book of essays - Obstinate Cymric (1947).
It includes an essay on Joyce's Finnegans Wake, which makes for an interesting contrast between two very different great novelists. Surprisingly, to me, Powys rates pretty FW highly, and specifically higher than Ulysses; whereas I regard FW as a shallow, tedious waste of time; whereas Ulysses, although mostly a STWOT, contains considerable stretches of wonderful prose.
But, (although I couldn't do it) it would probably be interesting to do a proper comparison of JCP's Glastonbury Romance, and Ulysses as two very different, worthy but failed, attempts at writing the Great Novel of the Twentieth Century. Both aspire to a kind of completeness of panorama; Joyce by going outward in all directions from the microcosm of three person's detailed perceptions and thoughts; Powys by distilling the macrocosm into persons.
I think of Joyce as pouring all his massive talent into trying to live wholly by-and-in Art. Plenty of others tried. All failed, although Joyce managed to succeed On paper - in the sense that he was able to write About people who lived almost-wholly inside Art. He couldn't remotely do it himself - and he was, indeed, rather a small and petty man. Which is the ultimate reason for his none-greatness as a novelist - he had the technique, but not the wisdom; could write like an angel, but had nothing to write about except his own resentments.
( A more recent version of the same combination as Joyce would be Saul Bellow.)
Powys had even more hang-ups than Joyce, or at least weirder ones; but he had a much larger and more complex soul and knew that the key issue of 'modern man' was his alienation; and that thoughtful Men yearned more than anything to re-connect with Life. Although Powys wrote very overtly about himself; he lacks Joyce's in-your-face-egotism, he is not motivated by petty resentments; Powys has that generous and appreciating spirit of the kind variously associated with Chaucer and Rabelais: he loves 'characters', eccentrics and odd-balls.
So if Joyce tried to lose himself in Art, to write from inside it; Powys tried to produce Art by spontaneous inspiration by drawing it from The World. Joyce was a consummate craftsman; Powys certainly wasn't, nor did he wish to be.
It is always a fact of Art, when judged at the very highest level, that it is constrained by the Artist. Only a great person can produce great art; and most of the best novels are limited by the limitations of their authors, rather than by lack of artistry. Neither Joyce nor Powys could produce wrok of the first rank for this reason - but while Joyce was limited by his nature, and could accomplish everything of which he was (in principle) capable; Powys was limited mainly by his competence - he was capable of a great deal more than he could actually achieve.