You are right partially as there is no limit to the prices of Bitcoin. Currently it says 21 million but more and more will mined and the limit will keep increasing . Then comes the price of Bitcoin . Who expect the prices of Bitcoin to rise upto 10 times the price past year. Infact now it's even more and there are many predictions which say that Bitcoin can easily cross 10k by the end of this year.
Yes bitcoin does not have a limited supply because many people are supporting bitcoin nowadays, BTC have finite supply of 21 million coins and that is a fact which is very well known.I do not know why you think that some alt coin which have "bitcoin" in his name can change total number of coins.Most of that alt coins even with "bitcoin" in their names will simply disappear over time.There is always a option to increase total number of BTC,but I think nobody wants to that happen.One of the reasons why BTC is most popular crypto currency is his limited supply among other things,and 1000 more new coins on market will not change anything.