Segwit needs 95% approval from miners(never going to happen) and only solves blocksize issues short term.
Segwit solves it long term because it enables for proper Lightning Network usage, which is the only way to scale to mainstream levels.
Lightning would take at-least 4-5 years to get activated. Also, it's an off-chain solution not on-chain solution which Satoshi advocated for. This means value spilling over from BTC into other more transact-able alternative currencies.
There is no way to do everything on-chain forever. If Satoshi wanted for all operations to be done on-chain so why did he invented block reward halving?
Block reward halving is a part of the Bitcoin algorithm that defines how the currency is supplied. Whereas in banks, they can issue currency at any amounts they so desire.
It has little to do with scaling, it's one of the things that makes Bitcoin decentralized.
The increasing volume of on-chain transactions (and therefore the fees) will (or at least should) compensate for the decaying block rewards. Which is why on-chain scaling is plausible.
PS: I do not support either SegWit or Unlimited, will support whichever wins.