How many entities control Bitcoin's network? 5 major mining pools?
Miners or miner pools do not control the network. Only theoretical threats from miners are DDOS or double spend attack (aka. 51% attack), but even with these attack they cannot change consensus rules. Nodes running Bitcoin Core control the network. At the moment there are approximately 44k nodes – these are the entities that enforce consensus according to which miners have to play. Every one of these can choose what version of Bitcoin Core they run and there's no way anyone can force an individual to run a certain version of Bitcoin Core.
Miners already pushed for a change in the block size with BCH fork, yet they failed to convince even such a simple change. Node runners as a whole are in control.