The current increase of Altcoin market cap at the expense of Bitcoin is not caused by coin inflation but it is the result of corruption among the Core developers who are deliberately suffocating their hostage (Bitcoin) until everyone agrees to their parasitic plans to apply corporate banking "solutions" (Lightning, SegWit) to the scaling problem. They could at least increase the bock size a little bit, but no, they even have the guts to claim that high transaction fees were actually good, while everyone can observe the steady decline of Bitcoin share. SeqWit is not bad per se, but not this way.
You are right that there is a limited amount of scarce commodities on earth and an unlimited amount of scarce cryptocoins. Yet I expect the network effect will not be equally distributed, so one coin will still dominate eventually, even if it isn't bitcoin and even if there are millions of alts. The almost univocal raise of any alt coin is the result of both, corruption and ICO hype. It will not last, regardless what happens to Bitcoin.