I'm probably going Oscar first here somewhat comfortably. I think he just had the most impactful peak with solid prime consistency and very good longevity especially relative to era. Elgee once said he thought Oscar's first ELEVEN years in the league he played at an at least weak MVP candidate level in his backpicks profile. I think that's a somewhat fair assessment with the data we have, and like I said even more impressive looking at that longevity relative to era.
Now Julius Vs Dirk is a little more difficult to me. Julius' ABA stretch looks extremely dominant, especially that '76 playoff run that looks like an all-time playoff season statistically, where he certainly looks like a high impact player. -i'm impressed by his offensive floor raising when looking at the pieces in and out from the Nets each year and peg him as a strong defensive player
We really don't have much film for ABA Julius(I think there were like 4 or 5 games i've seen from the '74 - '76 Nets available on youtube), but honestly when I watch NBA Julius he doesn't seem TOO different?? There is also a bit of reason to believe the strength of the late-ABA and NBA wasn't TOO significant at the time
https://www.backpicks.com/wp-content/uploads/2017/08/ABA-v-NBA-comparison.pngI do think the lack of 3 point line and his knees hurt him a little bit(not sure how much tho because he was elite in the 1977 playoffs), but the weaker NBA RS impact footprint(see Pollack's Sixers on/off data) is starting to feel to me more like a very non optimal fit situation supressing his numbers/making them look really inconsistent year-to-year.
It's also worth noting his impact rose in the playoffs in those early NBA years. '77-'82 Julius had a 4.5 OBPM in the RS and a 5.8 OBPM in the playoffs. Which is on the high-end of RS to PS translation for stars.
That being said I don't think peak Dirk quite matches up to Julius' relative to ABA dominance(?), and I gave some reasoning for why I may be high on his NBA potential - I think in other roster construction situations he could look alot better but whether that's really an argument for or against him(portability) is debatable.
Dirk may have an edge in prime consistency depending on how someone views '78 and '79 Julius.
Both have very strong longevity(i'd say both have maybe 10+ or so all-nba caliber years) but i'm probably giving Julius' the edge there because he played in the 70s-80s.
So to conclude i'm going to give Julius a very slight edge over Dirk here due to uncertainty but I could see that one going either way tbh, I may just be higher on Julius than most people.
Oscar > Julius => Dirk