I think altcoins just preventing bitcoin to evolve and grow maybe i am not right but that's what i am thinking.
No I don't think in such a way about the growth of altcoins. At times due to varying strategies altcoins profit high than bitcoin but this doesn't stop the growth of bitcoin.
I think alts are slowing bitcoin down a lot more than that.
one thing that is very common about altcoins are the fact that when they get added to an exchange, the price raises by a considerable amount.
now most of the time people can only buy newly added altcoins using bitcoins. so they buy small amount of bitcoins, trade said bitcoins with the new alt, alt gets pumped and multiplied their investments, then they cashes out to FIAT through bitcoin.