The Bitcoin Blockchain can only process around 5 Transactions Per Second (TPS) give or take.
When you compare this to VISA which has a TPS rate of 2000+ it seems very low.
If Bitcoin is going to become mainstream in the future the TPS needs to increase greatly.
Is there a way to increase the scalability whilst also maintaining a high level of decentralisation?
Payment networks always have more secure lower layers and higher less secure more efficient layers.
Banking system doesn't process 2000+ transactions, VISA's higher network layer does.
Just like Bitcoin can't process lots of transactions on-chain, but the Lightning Network can easily eclipse VISA tps many times over.
All payment networks are built in layers with final settlement and security on the lower layer and faster payments on the higher layers.
So if you're gonna compare Bitcoin to VISA, you have to do the comparison between Lightning Network and VISA, and the LN blows VISA away in speed of payment, tps, decentralization, and cost efficiency. LN of course is still a brand new technology and still has lots of work to be done on it, so I'd say security and reliability of payments and ease of use are still where its lacking, but in those other areas it already crushes higher level banking payment networks like VISA.