I've listened both Rogers and Davids new solo material and Rogers compositions still have that 70s Pink Floyd flavour while David hasn't sounded like Pink Floyd very much composition-wise. So I would hazard a guess that it was Roger who brought that famous feel to the Pink Floyd compositions. Also David himself said in the latest interview that it was Rogers project and it was Roger who was the gatekeeper and editor of all the ideas that went into the songs. I.e. he was the main songwriter.
When Gilmour said “That was Roger’s project” he was talking about The Wall itself, not Floyd as a whole.
Rick Wright, Nick Mason, David Gilmour and Roger Waters is what brought that famous feel to Floyd, not any one member.
As for Roger’s recent work sounding more Floyd-like, that’s because that dude relies on guys to deliver the best Floyd playing/sounds they can and is precisely why he’s had Jon Carin as his live musical director for a while now. Carin did the ‘87 and ‘88 Floyd tours and played on Momentary Lapse and The Division Bell, had a falling out with Gilmour in the 00’s and immediately started talking shit about him after Waters hired him, claiming he wrote some songs he wasn’t credited with, then miraculously Gilmour was able to post the demos of the songs Carin claimed were his, recorded before Carin was even involved.
Gilmour hasn’t wanted to do the Floyd thing for decades now. He didn’t even want to play a ton of Floyd songs on his recent tour because he’s been ready to move on from that for years and stated as much before the tour, much to many fans dismay. I’m good either way, Gilmour can play any song and I’ll love it because there is none higher on my Mt Rushmore. He specifically worked with a producer on his newest album who didn’t give a fuck about Floyd to further get away from doing Floyd sounding shit.
Listen to Waters’ demos of Floyd tunes before the band got a hold of them, they’re all basically folk blues tunes-
When he did the demos for The Wall they had a bit more Floyd sound to them, mainly due to him using synths to make the majority of demos, but still, didn’t feel or sound like Floyd until the other dudes showed up and did their thing. Even “Young Lust” was a folk tune before they came along.