Now when one says "weaker", what exactly are you meaning by it?
For me, it depends on what the purpose of the album opener is.
If it's meant to draw you in, then I can see it a bit.
But, also, the Mangini era album openers are in fact their singles. And all these openers in fact, sound alike to me, and this started once they made Constant Motion a single. After that we got A Rite of Passage, and it has a similar structure to Constant Motion, solo section included, but with a JR high note bend instead of a JP whammy bar note bend. Since then, each single has followed a certain type of structure, and sound, OTBOA/TEI/UA all have a similar sound and structure, although Untethered Angel doesn't really follow that style as much as OTBOA/TEI/AROP/CM do.
Untethered Angel, is the first single where I thought, ok, this is the single song, and the one that will open the forthcoming tour, it's not bad, it's ok. The meat is what comes after. And with D/T, they made all the first 3 songs their singles. I think they made this track-listing like this to draw in the newer casual fans. To me D/T has a nice flow going from their single, metal-style type of songs, into their more obscure. Pale Blue Dot is a great closer, and one of their songs with a more obscure structure. It's not their usual epic style album closer either, this album closer is more of a closer that doesn't resolve, but keeps you in suspense, like being left floating in space.
I wouldn't include The Astonishing in this at all, due to it being a concept album, and it's the same with SFAM.