Only reason ETH and Dash are this big right now is because of BTC fork drama, spooked crypto enthusiasts look for safety in what they perceive as the next best coin and plan to go back to BTC once the drama is over. 90% of people dabble in alts to increase their BTC stash, that's their one and only goal. And it only takes a small percentage of scared Bitcoin fans to inflate certain altcoins to huge bubble proportions. I'm not a Bitcoin maximalist, I'm sure a few altcoins will find their own niche in time, but right now they're simply way overvalued due to the Bitcoin drama.
I disagree. ETH has really many more uses than BTC, it is more interesting, will attract a more diverse crowd and support a more diverse ecosystem eventually. The only problem with it is the big supply with inflation that is still not definitely defined - it makes it kind of less attractive to those very people who push the price up - the investors. Of course bitcoin can still attack this space with RootStock - but currently this seems very remote. With DASH I am a bit more sceptical - but it has also innovated. DASH has somehow better privacy - but it also nailed down the social system with the DAO idea - the result of it is for example paying the PR girl, this also is a big innovation.
Without question there are many alts whose genetics are better suited ,than Bitcoin, to all kinds of uses. However, the first mover has a huge advantage of brand, network effect, and simple holder/user inertia.
Bitcoin's advantage will erode amongst the Crypto community (indeed that path is well advanced now), however, it is the global currency/transaction market which will drive new adoption, as that is fresh money, and big scale. The highest profile Crypto will benefit from new attention, and that is still BTC. It is also the defacto settlement layer in most altcoin transactions.
Things may well change, but the process will probably happen in political time (think years) rather than tech time (think days). Like an environmental ecosystem, new species are competing for a niche, against dominant creatures. That analogy might suggest the possibility of a quick tipping point, but equilibrium remains the default state for the majority of the time.