You want to say that if all miners establish the highest possible exchange rate among themselves, this makes the system more centralized. Judging by the number of orphan blocks, the miners have achieved this goal. That is, at the moment, the miners are as centralized as possible in terms of the exchange between them. It is simply impossible to make it more centralized already. 
Hmm. I recall certain pools don't have direct connections to each other and were resorting to running zombies on each other in the past. I find the current stale rates fairly reasonable and mining pools don't necessarily have to resort to those tactics to improve their propagation. If we were to reach the state whereby blocks takes 50 seconds to propagate, then is it possible for the major mining pools to strategically exclude others from their exclusive "subnet"? Yes, spv mining has risks for the miner. And the miner himself decides whether to use it or not. And if you claim that it is impossible to increase the block in order not to encourage miners to use spv mining, then this is one of the most ridiculous arguments against increasing the block.
I don't think anyone has ever claimed that. On the contrary, we have proven that full validation is sufficiently fast that the benefits of SPV mining is slim to none. The problem of SPV mining is that it is two fold; the incident caused a longer than usual block re-org and the damage could've definitely extended beyond the users.