So, some thoughts:
I do think we see a pretty clear drop in motor from the ABA game to the NBA games, and I think that likely mattered a good deal. In the NBA games I saw so many transitions on both ends of the floor where Gilmore wasn't in the play. Sometimes I'd see his teammate start to run and he'd just be walking until he fell behind the camera's gaze.
I think that both in the ABA & NBA Gilmore seemed to have spotty awareness. It was almost like he was a security drone that would get "turned on" at certain points, and when that happened, you were in trouble. Try to challenge Gilmore directly and you were likely in trouble. Get the ball to Gilmore in his wheelhouse and he was often unstoppable while displayed nice touch and skill.
But on the other hand, there were times where it was like he was thinking "I'm guarding my man" when it really seemed like he should have been able to leave his man and block a shot or get a rebound. Additionally, he seemed fairly easy to take out of the play by having the man he was guarding drift away from the action - in fairness to Gilmore here, this is the whole conundrum of what to do as a big man when the man you're guarding has range, but with Gilmore there's a feeling that he wasn't so much balancing threats so much as he was just following his man around, and there were times where he ends up literally guarding a man on the perimeter.
I will say that I think Gilmore showed good movement and body control, and when he was out on the perimeter he didn't seem like dead meat at all, but he left a gaping whole by the rim.
Gilmore didn't seem comfortable trying to use his body to push other guys out of the way. I think that some of that is that he didn't have the widest frame and so it wasn't the case that he could just bump into other guys and send them flying. But there was also this tendency to let other guys wall him off, both from the opponent and from his own teammates. If he saw an opening, he'd fly in there and get the block or rebound, but when things were congested, he seemed bottled up.
I find myself reflecting on this conundrum:
How is it you can have a shot-blocker as good as Gilmore, that everyone knows controls the rim area when he's around it, and yet not seem to have much effect on opponent eFG%? Not saying he never had an effect, but as we go through the years, Gilmore seems to have a bigger effect on things like defensive rebounding or free throw prevention than he does on making guys miss shots. Why is that?
I can come up with theories plural, but I don't have confidence that I really understand what was happening.
I think myself thinking that Gilmore would have faired better in an age with more space, where "better" here means that he'd scale better than most other classic big man anchors. The spacing of the NBA has lowered the effectiveness of big men in general, but aside from the fact that Gilmore had a decent shooting stroke, and quickness in short bursts when traveling along a straight line which would allow him to have horizontal impact on defense, and I think it would simplify the traffic on the interior and make it easier for him to navigate.
Hey: With what's going on in the world, my fuse is shorter than it used to be, and it's leading my lose my cool and then go on self-imposed breaks from things (such as RealGM). Please try to keep it civil, and I'll be looking to do the same.