The fact about altcoins has always been that they are ALWAYS getting dumped over the long haul. The ONLY reason why they show gains in terms of USD is because bitcoin price is rising and nothing else.
All of them are useless and majority of them either have unlimited supplies (natural inflation) or enormous supplies which does the same thing.
If bitcoin were to become stable today and remain stable for at least 6 months we would start seeing what the real bloodshed looks like in altcoin market. It should remain stable for long because for short term stability altcoins get massively pumped, for example when bitcoin stabilizes for a month people start pumping altcoins but after that the dump continues and since bitcoin price is stable the altcoin prices in both BTC and USD continues dropping. But luckily for altcoins bitcoin USD price keeps going up and it masks the fact that they are dumping against BTC by showing small gains.
Keep in mind that it would actually be a net gain in altcoins IF their price went up as much as bitcoin price did or more. But when the USD gain is smaller than BTC price rise it shows that the net gain was negative meaning they are indeed dumping.
For example if bitcoin price goes up 10% the altcoin USD price should also go up 10% (remain stable) or 11% (gain value) and higher. But when it goes up 9% or less that shows that the altcoin was actually dumped.