My opinion is that eth will get replaced by a new smart contract technology in the future.
Do you have any proof of this happening? Any specific projects in mind? Better leaders? Better team?
It can happen if theres a big project like what you said but it will take time and maybe it wont happen at all. We should not hold a coin forever, we should trade it and take the profit and if theres a new coin to invest for then buy because its your goal to increase your profit. Right now I still see the dominant of ETH over the altcoins and it will stay on that position for the next 5 years.
To trade Altcoins, you need experience and knowledge. Because 90% of bidding will bring you losses. Trading needs to study for at least 2 years. I am a supporter of long-term investments in cryptocurrency.