It is true that Doge started as a joke and has been considered a "junk"coin for most of its existence.
It is also true that Doge doesn't serve any purpose other than as a store of value.
And yet, where most other altcoins have foundered and faltered, Doge has made it through the years relatively unscathed. The reason as you have so rightly pointed out, is due to the fast transaction time, relatively low price and transaction fee, and its prevalence in the crypto-verse.
Doge will survive as long as people continue to trade on exchanges.