I really think it's misguided when people default to H2H raw stats to see who outplayed each other in 4 games. Kareem's game was totally different than Walton's game. His role was totally different. It's not a question of who scored more points, it's a question of who impacted the game more. And Bill Walton was totally doing his thing in that series. (Not that I would even point to 4 H2H games as a determining factor in deciding who was better).
Beyond that though, and this is discussed extensively in the 77 RPOY project thread, I think Walton (healthy) was better than Kareem (healthy) that year, and it's nearly impossible to find a better year for Kareem. As realbig3 said, Kareem IS the second best offensive center ever. But he accomplishes this not with tremendous global impact and by ignoring his own impact, but mainly because his own individual impact is so freakishly good. In this sense, Kareem at his best will look better in the box than just about any center ever. It doesn't mean he's necessarily better, mainly because of...
DEFENSE.* Kareem is really good on defense. Walton was a
monstrous defensive player. To me, the best defensive impact player since the merger perhaps. Incredibly high motor, incredible rotations, shot blocking and great rebounding. Then on offense, he turns O into D with GOAT-level outlet passing, but he's also a highly functional mid-post hub. This is similar to the role 67 Wilt was playing, only Walton is a better passer and has a better mid-range jumper.
None of this is to say you're crazy or "wrong" if you think Kareem's peak > Walton's peak, but it's not hard to see how people would see Walton's as over Kareem's and thus behind other big men they see on par (or better) than Walton. But again, it certainly doesn't make sense to frame this debate by looking at raw box stats.
As I've posted before:
77 Walton -3.4 to +7.9 SRS (18g)
78 Walton -2.8 to +9.5 SRS (24g)
75 Jabbar -4.2 to +1.4 SRS (17g)
77 Lakers after Washington injury were -0.9 SRS (28g) +4.5 before
78 Jabbar -1.7 to +4.1 SRS (21g)
So chew on this:
The 77 Lakers were +4.5 SRS around
Big
Ford/Washington
Tatum
Russell
Allen
The 77-78 Blazers were ~+8.5 around
Big
Mo Lucas
Gross
Twardzik
Hollins
But this also means the 77 Lakers played sub-.500 ball for more than a third of the season without Washington. It's no wonder they were swept by Portland. Heck, it's impressive they beat GS.
*If you're thinking, Portland's defense in 77 was only -1.5 and in 78 -3.7, understand that Walton was injured for 25% of the games. In 1977, assuming a constant pace (highly unlikely), the Blazers DRtg would have been -2.2 w Walton. There is extensive discussion about how much faster they would play with Walton, but let's still assume they were behind the fastest teams and played at a 110 pace (up only slightly from 108 average) with Walton. That would make their DRtg -4.0 in 77 w/Walton.
In 1978, as we'd guess, the results would be even more pronounced. Portland would have been -4.5 with Walton in the lineup if we assume constant pace. Again, this is highly unlikely. Simply making the pace league average w Walton would change the defense w him in the lineup to -6.8.
For reference Portland's 1977 PS DRtg was -5.4 in 19 games. Their 1978 PS DRtg, without Walton, was +2.3 in 6 games to Seattle.