Didn't we see this, to a lesser degree, in the last bull run?
Bitcoin initially got the influx of funds, but as the bull market matured, those funds found their way to "the alt coins", which exploded. In the downtown, Bitcoin was a safe haven (like gold in a precious metals bear market). Now that we're back in bull mode, bitcoin is taking the initial influx of funds again, but I don't expect that to continue. As investors look deeper they'll see the pros and cons of each crypto, and "diversification" will become the mantra, as Bitcoin's dominance falls far below 50%.
The long term trend is for Bitcoin's dominance to fall from 100% toward 0% (but stabilize at some point before then). Where exactly that will be is yet to be seen, but I think it's a fair bit lower than where we are now. Bitcoin is enjoying one of its last moments in the sun, although it will always be around to some degree or another.