1st) Ripple is not a cryptocurrency and for Ripple company and all of their structure and clients, the pair XRP/(any other thing) is irrelevant, right? Right! It is true that many guys from this company get a lot of money with the recent overvalued XRP/USD! It is true that what happen caught a lot of attention with a new clients! But, even all os this, the Ripple's product suite works well regardless of the amount we attribute to the XRP/USD pair.
2nd) Is a centralized coin with control in the hands of few people. A small group have the true control of this token. For how much time they keep the tokens free for our use? How much time to change the rules? How much time for manipulate as they want? It is a complete private coin borrowed for all of us trading for while, for now, and after?
3rd) The problem with scalability of Bitcoin demand for a solution that Ripple already has. Because that, the value of XRP went up a lot. But, now, we have the lightning network works very well, not? Yeah! Even that, we can use Ripple protocol for transact not only bitcoin, but a lot of other digital and fiat coins. Ripple is not a competitor for Bitcoin and others.
4th) See: 'https://www.fool.com/investing/2018/01/25/3-reasons-ripple-investors-should-be-very-worried.aspx', and you will understand why a centralized coin will never be consolidated. It's not only a opinion, it's logical! One man is weak, one man is unstable. Change a mind is easy. To make significant changes a decentralized coin is very hard, and this is very important and brings security for users (investors or who just use for simple payments).
5th) I really believe that the PoW will be replaced by prof-of-something better, something equally secure and more efficient, making transactions cheaper and faster without the need for additional networks or schemes.