I am a fan of Roberson, and sorry that his senior season has unfolded this way, given that he was such an important cog in our postseason run last year.
But I agree with everything you say above. Roberson's biggest issue IMO is that he's so limited. He's a 6-7 guy who has played around 210 pounds his entire career, until this season when he noticeably put on some muscle. At that size, he's too small to play center [unlike Lydon], he shows zero defensive aptitude despite being a multi-year starter, and he's a negligible shotblocker.
If he's been able to slide over to center--say, if he were more like 6-9 and a shotblocker who could patrol the middle for us--I think his career would have been completely different.
And this year, JB not only has Lydon but also another capable 4 in Taurean Thompson to utilize. So he's not locked into the one-dimensionality of Roberson anymore, like he was last season. It's unfortunate, but Roberson could still carve out a niche if he played better. Not singling him out given that the entire team is underachieving, just pointing out that Roberson isn't making the case for additional PT with his play.