Increasing block size is not a sustainable solution for scaling transactions. Transaction fees are too high and BTC should move to 2MB as a short-term fix but the long-term fix is off-chain solutions like Lightning.
Bitcoin Cash scale what it can scale, that is, blocksize. That's it, it is a pragmatic approach absolutely obvious for anyone with more than 2 year of experience in programming.
A side-effect of SegWit is a partial increase to up to 4; the average block size is already above the previous limit of 1.
That being said, the least sustainable solution is to keep blocks at 1 MB for btc. The core group have ousted and alienated everyone who made bitcoin work originally. The fees have priced out everyone who created the ecosystem originally. It is crystal clear to anyone even slightly paying attention that they have done nothing but lie and censor.
If you are getting all your information from /r/bitcoin you should know that it is censored into oblivion and has been nothing but propaganda for years now. Bigger blocks obviously work and the 'lighting network' not only has raises enormous questions about how it can work, it has been promised as just around the corner for multiple years now.
[0] This actually happened a couple of times earlier, but those were fixable with straightforward software optimizations.
The bottleneck is propagation time. Also "The propogation time did not depend strongly on the network bandwidth for the given nodes"
Keep in mind that it is not sufficient for each node to have the bare minimum amount of bandwidth to download 1 block every ten minutes. When a node mines a block, we need that block to propagate across the entire network (~11,000 nodes [0]). Further, we want this propagation time to be relatively trivial; otherwise the number of orphan blocks would increase giving an advantage to large mining clusters and reducing the overall security of the network.