In what sense?
Dynamic time or weather? Nope. PCARS has both. All we've heard so far is that they plan on including selectable time and/or weather variations that will remain locked throughout the race. Which is what FM6 does, too.
Locked framerate? Nope. Forza Motorsport has been running a locked 60fps since 2011 on the 360.
Car list?
Track list? By your own admission, FM5's list was poor. GTS is launching with barely more locations (14 vs 19) – again, 3 years later – but with a much smaller ribbon variation total (40-ish vs 27). Every track in the Forza series is laser-scanned (outside of their fantasy ones, obviously). The same can't be said for PCARS, but it does have a whole heap of enticing circuits (I don't have a count on me). AFAIK, every circuit is laser-scanned in Assetto Corsa, too.
Cars on track? Nope. 20 so far for GTS. 24 in FM6, and something over 40 in PCARS.
Modifications? Remains to be seen. Given the eSports bent, I seriously doubt we'll have much, though.
Tuning? Remains to be seen.
Livery Editor? It may end up better than the ones in Forza or NFS. We likely won't know until release.
The two big things I see GTS having over the genre? The FIA certification, and a deeply impressive photo mode. The first of those has little to do with the development of the game (it reads largely as marketing). The second is very cool to someone like me, but is admittedly not a 'core' feature.
I think it's a disservice to other developers to suggest PD does more than any of them. They do things
differently. That's all.