If by top LW you simply mean top 15 range, then yeah I'm in agreement. If you mean he'd be the champion, or damn near, I'm not so sure.
Quick look at the UFC LW Top 15 tells me that there are some guys he'd beat (I'd be down with a Poirer rematch at 155, holy shit) but I think he'd really struggle once he moved toward the top 10, although LW isn't quite as bad for him as it once would have been (back with all the strong wrestlers, the Maynard/Edgar era).
I don't think he has a prayer at WW though, just too many big dudes who can take his punches, land their own, and grapple him to death.
I checked out on the betting for this one once it became Diaz, just wanted to soak it all in as a fan. I think RDA would have absolutely trucked him though. Chucking bombs or not, Conor was still fading quickly at the end of the first round and that is very concerning. Personally, I am very interested in how he fares against Edgar, as well as a rematch with Aldo. I would definitely enjoy a rematch between Aldo and McGregor, though I'm of the belief that Edgar deserves first. Admittedly, I will accept that the "bigger fight" for the UFC is likely the rematch, and the Edgar fight is much more dangerous for Conor, so I suspect that's the way it'll be going.