If dumpers can dump coins and tokens in a reasonable way it won't affect the value much , lose in value when dumping happens if a dumper dumps huge amount of the token at once , this is a wrong way to dump coins, this is why till date some devs put locks on their tokens ,some even release percent by percent on term basis just to avoid huge dump.
The best way to dump is not to dump in an instant or a whole at once
The dumpers will never try to dump it at once when they are not feeling panic about that dude, in fact, that the dumpers wanna get the high price by liquidating their amount slowly but the problem is there was on only a single person who dump the market.