Exchanges don't accept sumo to buy in, so you have to dump a lot of sumo to get BTC... this will dump the coin like heavy... don't you think so??
Usually, that's not something that happens. The team uses the money from their own pockets (instead of just dumping the coin on which they're currently working upon) and then, once the coins (or the "pre-mine" in this case) are of good worth, they dump it.
...but yeah, if the team who's managing the project is poor, that makes a different story.
There's no guarantee at all that they won't dump it...most especially when an unavoidable factor called "human nature" is in play.
Greed is the real human nature, actually. That's why most of the pre-mines are kept until they're really worthy of getting dumped.
Dumping pre-mine right now won't make any sense, first the project needs to stand up in a better position, then the pre-mine should get dumped.
There's a real lack of volume for Sumo, a better exchange (with good volume) is definitely a requirement right now. Cryptopia is just not enough.
https://whattomine.com/coins/196-sumo-cryptonight
The mining difficulty at whattomine - is it really accurate/updated?