As I mentioned Bitcoin Cash tries to see how far we can go with on-chain scaling.
Bitcoin on the other hand mostly avoids on-chain scaling and wants to add on side-chains which are supposed to scale. They're basically a second blockchain but it works a bit differently with different security trade-offs and comes with easy on and off settlements.
Monero wants to make all transactions private and thus make the coin itself fungible. The trade-off is that it's much harder to scale than the transparent blockchain of Bitcoin.
Ethereum wants to explore the idea of having advanced smart contracts on chain and again have several hard problems ahead.
Which approach is the best? Who knows...? Maybe in the end we'll have one coin that integrates all breakthroughs or they will each tend to their own niche. Overall I'm quite hopeful (obviously).
Now surrounding all this we need a lot of plumbing services. Payment processors which can accept the different coins and exchanges that makes it easy to swap between different coins.
I'm not sure if that answers your question though!
Also we can already achieve PayPal like transaction amounts today, with Bitcoin Cash having in practice 20% of throughput. The limiting factor to scale further is software limited, not hardware. Furthermore it's possible to reach VISA levels of throughput with further work.
Scaling is one of the hardest issues for sure, but dismissing the viability of cryptocurrency because of it is naive.