it is all in the distribution model they choose. it can be through mining reward with a good rate and create a nice growth like bitcoin. or it can be a bad distribution with large rewards and no cap,... and put the coin on a never ending downward trend like Doge.
or it can even be PoS rewards, or premine but distribute 100% of it although this last one is hard.
Nothing is perfect. But being mineable is the best distribution model and the best model to get a wide spread community who strenghten the ecosystem. And as you say in your "last one": a pre-mined coin will never be distributed 100% (or 90%, 80 or 70% as it will stay in one hand) and the main problem is the fiat-money character of pre-mined coins. As the mining-process of these coins is always in just one hand they're always in danger to undergo inflation because no one could limit the creators coin production.