.. snip...
I was working on a long response and just trashed it all.
So let me re-iterate in what I hope is the simplest way I can. Your statement is that full nodes have zero power, "zilch" so they might as well "all" be shut off. The "full nodes have zero power" is what I'm talking about, not your statements where you start to add qualifiers. You have failed to convince me that it's true.
Let's just use an example where 75% of miners want to increase the emissions back up to a starting point of 50 coins/block.
The market won't like that but they have no ability to reject that protocol change. They might drive the price into the tank for awhile, but they've proven time and again that as long as they see they can continue to make money, they'll do so and so will end up just accepting it.
Full-nodes however, can reject those blocks, accept the 25% and bring about a split in the network etc.
But this is your error:
non-mining full nodes don't have to reject or accept this. The miners themselves (the miner pool nodes) already did.
The split was already there when the miner pools split. There were full MINING nodes broadcasting each of the chains, and these are the ONLY TWO SOURCES of the two chains that exist.
Let us call the, say, 6 pools that make the 75% "50 coins" chain, chain A and protocol A, and the 12 pools that make the 25% old protocol chain, chain B, and protocol B.
My statement is that indeed, all non-mining nodes might just as well be shut down, from the moment that the pools have sufficiently strong data center full nodes that everyone of us can connect to them directly.
Suppose now that you have an SPV wallet, and let us presume that the split doesn't affect the communication with the SPV wallet. If you connect your SPV wallet to one of the A-type pool nodes (MINING nodes), you will see your havings on that chain ; if you transact, you transact on that chain (let us presume that something is in place to avoid replay attacks, like a version number or something that alters the signatures). For instance, you can send them to an exchange that lists both coins, and sell them for LTC.
However, if you connect your SPV wallet to the B-type pool nodes (MINING nodes), you will see your (initially identical) holdings on that chain. Your coins will still be there, even though you sold your A-type coins for litecoin.
Of course, if Joe, your neighbour, has a full node that he configures for protocol A, you can also use his node, that copies the chain from type-A pool nodes ; and if your other neighbour, Jack, has a full node that he configures for protocol B, you can use his node that copies the chain from type-B pool nodes. But they are just copies of the one or the other. If Joe and Jack aren't there, you can directly connect your SPV wallet to the sources of these data without using them as a proxy. And if you feel like it, you can run both nodes in your basement, and copy both block chains. But the only sources of chain A and chain B are the type-A mining nodes, and the type-B mining nodes. You can get copies if you want, or you can use copies from neighbours if they are around.
Now the market has the ability to ultimately make the final decision. Yes, there will be chaos and the outcome would be unknown, but now it's in their hands.
So that means full nodes have zero power?
Yes, because the markets didn't need non-mining full nodes, as they could do it with the mining nodes that are the source of the data and are the processors of transactions in any case.
Now, this is an interesting market, because the miners of A have 4 times more coins than the miners of B for each block. So if the market would split into putting 4 times less value on coin A than on coin B, the miners would eventually switch to a 50%/50% hash rate split, because then, earnings per hash rate are in equilibrium again. In order for the 75% / 25% split to be maintained, coin A would have to have more than 1/2.3 the market value than coin B.