We need to combine many possible option to increase transaction throughput, whether it's block size increase, signature aggregation, LN or even different cryptography which have smaller signature size (obviously while remain secure).
These are all only incremental improvements though. Even if block size increases by a factor of 5 - which I know almost no one on here would support - and signature aggregation techniques further improve transaction density by a factor of 5, assuming we have a billion users, each user would still only be able to transact on-chain - e.g. to perform a channel open/close - once every 80 days, which is still very tough.
We really need a 1000x improvement.
Each of them may only increase by a factor of 5 (example number), but if you combine them you could get 25x improvement. Obviously it's not enough to billion users, but i'd take small improvement over nothing. Besides, IMO it's just matter of time before block size is increased and it'll be faster if Bitcoin community want higher transaction throughput.