After a hard fork, even there are only 4 people hashing on the original chain with old client, it will quickly develop into a popular chain and most possibly knock out the new chain
It is a no brainer: One chain has limited resource (expensive), another chain has abundant resource (cheap), btc on which chain will worth more?
To answer your question, the one that will be worth more will be the one that people trust in and use.
If one has 4 people securing it, and the other has thousands of people securing it, which do you think people will trust in more?
Trust is everything in a currency. But the number of people securing it is a dynamic variable, subject to change over time based on confidence and expectations.
Allow me to pose to you a different question.
Assuming a fork, which of these blockchains is more trustworthy:
Chain 1: a coin which has
low transactional capacity, but which is subject to a single kind of manipulation based on 51% processing power accumulation.
Chain 2: a coin which has
high transactional capacity, but which is subject to three kinds of manipulation: 51% processing power accumulation, 51% bandwidth crowding out, and 51% storage capacity crowding out. And which possibly requires human debate and intervention (reforking?) every few years to set an "optimal" block size.
As a long-term saver, I know I would stay with Chain 1, even if it had fewer miners initially. And I think you underestimate the number of people who value security and decentralization much more than transactional capacity. I'd predict that over time, as people understood that Chain 2 has more attack vectors than Chain 1, they would migrate their savings over to Chain 1, leading to a much higher valuation for Chain 1 over Chain 2, regardless of the fact that Chain 2 can potentially process many more transactions per second.
High valuation for a currency does not come from transactional or commercial use, quite the opposite, it comes from the percentage of the monetary base that is withheld from the market as savings. That percentage is the true measure of trust in a currency (the higher the better). Gold has already proven this conclusively, with a $1500 market value in spite of virtually zero commercial transactions per second, and virtually zero merchants accepting it as payment.
Would Bitcoin trading at $1500 with 7 max TPS be a failure, or a giant success?
There is nothing to fear from a limited (low) TPS. It is a tradeoff for guaranteeing Bitcoin's high security and reliability as a long-term store of value. Savers should not be sacrificed to accommodate merchants and bankers. I think that's what the message embedded in the genesis block is all about. The world desperately needs rock solid secure undebaseable savings vehicles for the little guy. Ask Zimbabweans, Iranians, Argentinians, etc.
BTW I'm not opposed to increasing the block size gradually and conservatively as average storage/bandwidth improves, but I'm opposed to the idea of overdoing it based on unscientific hunches, or the false narrative that Bitcoin will go extinct if TPS is set too low. Again, look at gold to see the resounding succcess of a 0 TPS monetary unit.