Only real scaling solution is off-chain. Think about it: how many more people have yet to get into Bitcoin in the world? How much would the blockchain (and block size) need to grow if they'd all use on-chain transactions all the time? It will need Gigabyte sized blocks, thus centralizing all nodes and defeating the whole purpose of Bitcoin.
Heck - even on-chain transactions these days partly use 'off-chain technology' when using SegWit to keep nodes easy to run.
That's the point though. We don't have to be using off chain, and the block size on chain will likely have to increase in the future. Storage is increasing year by year, and as a result is becoming cheaper. While it might centralise nodes a little bit, we can increase the block size in accordance to the affordability of storage, and its future outlook.
I agree that Bitcoin blockchain is growing slower than the decrease of SSD prices, but I don't think it can accomodate for 7 billion users doing transactions daily, except when using unreasonably ginormous blocks, while off-chain solutions do allow for this functionality.
