I both agree and disagree with your point about top coins. I agree that not all that top 10 was there and some of them will go down ...
However I also disagree that coins like ETH could ever come down...
I mean look at ETH for example, it became second biggest and it doesn't look like it is going to stop anytime soon with how they are improving to stay relevant.
I have no disbelieve in ethereum been a very successful coin. It's currently the only coin worth investing in my opinion after bitcoin and the upgrade coming up now on 3 December, is another major reason why it's advisable to get your hands on them while it's still affordable but when the issue if top 10 are brought into the discussions, coins like ethereum can easily be outperformed.
Let me reminder you that few months back for a very long period of time, ethereum lost its second position to ripple before regaining it after ripple failed to deliver. Now stablecoin are getting the volumes in regards to traders trading them and was reported they became the most traded coin as one point with in last 2-3months. Earlier this year, it was reported that
Ethereum’s value transfer Is now dominated by Stablecoins. and also became the most valued coins even ahead if bitcoin as sine point.
Ethereum is current profiting from the FOMO of its upgrade, sooner the hype was die down and if things are to get tense in the space like the introduction of cryptocurrency similar to what facebook's Libra tried achieving and the stablecoin volumes increase, we'll be seeing new coins in the top ten.