If the target is everyone (billions of people) using Bitcoin, using the blocksize to grow is not possible. Blocksize is not a scaling solution, it uses resources at the same scale whether it's 1 MB or 100 MB.
Blocksize is not a scaling solution
on its own, but should still be part of the solution. We need everything and the kitchen sink. SegWit, Blocksize, Lightning, Atomic cross-chain transactions, sidechains/treechains, etc. People generally understand that the blocksize is one of the more costly elements of the formula, but we still have to find a balance. Scaling 100% off-chain runs in stark contrast to the underlying principles of an open and permissionless system. Users won't stand for it and won't allow it to happen.