Transactions are an innate problem of Blockchain. A big downside, so to speak. The more transactions there are, the more time and money is needed for them to be confirmed. And I think your Visa info is wrong. From what I see it's around 1.7k transactions per second, not 45k. But let's return to cryptos. The only thing you can do with blockchain is trying to increase the number of transactions a coin would be able to process in advance. But the main problem with more transactions requiring more time and money will always remain. DAG, on the other hand, is designed in the opposite way, with confirmation stuff being tough at first, but getting better as more transactions occur. I believe this article and an image in it is useful to understand it: https://steemit.com/cryptocurrency/@steemhoops99/transaction-speed-bitcoin-visa-iota-paypal/