Again, I'm not insinuating that the GM guys snuck into the Ford engineering lab or had the Russians hack the Ford computers.
I'm just saying that in comparison to a traditional SBC head, the LS stuff (most especially the LS7) is pretty closely related to a Cleveland head, where no other OEM head is.
The poor exhaust flow is just the inherent nature of some cylinder heads and it's not really related to bore size. Take a close look at some older Pontiac heads. The exhaust flow is almost 80% of the intake on some heads, and some of the early Poncho engines had some very small bore sizes: the 350 had a 3.875" bore....the 389 was a 4.060"....421 SD was a 4.090".
I've seen some high 60% numbers on some LS7 heads, which requires a larger amount of exhaust duration to crutch it.
As for port volume, it will depend on the size of the engine and the application. The 4V Cleveland head was a complete dog on a factory 351 or a 302. It takes a lot of rpm (or extra displacement) to get that big 245 cc of air moving....
Like you say, most every performance automotive engineer out there will be familiar with combinations that performed well through the years. It's hard to start with a clean slate and not take notice to things that really work or were highlights of past decades. In my mind the LS7 is a pretty sweet piece because it has enough displacement to pull on that large intake port volume and a large enough bore to take advantage of the larger valves. Both of those are Cleveland traits, but the factory Cleveland engines were really too small to really take advantage of them.