Keeping small max block size doesn't solve the decentralisation issue (decline in node count). At very best it only slows it down.
Correct. I never implied that it does solve it. However, an increased block size limit could only make it worse.
People who run nodes don't get any direct incentive + most newcomers will go straight to lightweight clients or online wallets for convenience, so here's the real problem.
Well, I don't think that the majority needs to bother with using non lightweight clients. However, they should have the option to easily use one if they wanted to.
Yes. But to be fair, the main concern in blocksize debate is network bandwidth capacity rather than just storage.
Both are a concern.