None of all this is going to happen. Miners want small blocks and a fighting fee market. The cartel you are talking about with large blocks only sets in with such incredibly large blocks, that they are out of the question in the next few years ; if you want a mining cartel, the telephone between mining pool bosses is a much more useful device than multi-GB blocks that saturate small miner's network links and most of the user nodes.
You
had a mistake in your concept of propagation through the network. You are thinking a decentralized network is a fully connected mesh topology.
You don't need that much larger blocks to cause an amplification of propagation delay to the smallest miners in order to destroy decentralization and take 51% control. Also it only requires a very small advantage in relative orphan rate in order to slowly accumulate more hashrate than the opposition, so don't require the 100GB blocks you are computing.
Bitcoin is already centralized
Yes in that case they don't need huge blocks to destroy decentralization because it is already destroyed. In that case, they need to be able increase blocks to whatever they think is the level of transaction fees that maximizes their revenue (volume x transaction fees).
In either case, I am showing that big blocks are a cartelization paradigm. I am being thorough. Please don't fault me for being thorough, just because the network is already centralized.