I wouldn't say other cryptos have an equal opportunity. Bitcoin is the first, the most accepted, most popular, most secure, most computationally and financially invested, most recognized blockchain. There is not that much space for the second. The idea of currency is that it is accepted by as many people possible and Bitcoin is it right now. It is very hard to take that and there is no real reason for people to switch. It is a simple and secure application, reviewed many times. And there are crytpos that are there from 2013 and still quite popular, but they are not even close to Bitcoin. Bitcoin was not surpassed in more then 8 years. So in near future, I really really doubt it. In long term, maybe, but I wouldn't bet on it. Bitcoin is simply good enough and it would be a huge cost for people to change it.
I agree with your points. What I understand from your thoughts are that they are practically monopolizing the industry right now. The thing is that it is technology at the end of the day and can be replicated in terms of availability, security etc. Classic case being Iphone. Now Nokia was well established as the leader till Iphone came alive in 2007. It helped that it came from a successful family and the quality ofcourse.
So maybe it may take someone from a different field which has good background to get into cryptocurrencies and grab that share currently enjoyed by Bitcoin.
It is more then that. Bitcoin isn't just like a new smartphone. Bitcoin is a network. If you buy a new Iphone, you can still communicate with people that have an old Nokia and they can with you. That is because the protocol used to make calls and SMS are very old and still used today. There are better protocols, but it would make new people disconnected from the old. Same is with Bitcoin, it is a protocol, not a shiny new device. People accept Bitcoin as a payment and not other coins. If you start accepting other coins, then you will have trouble using them, since others don't accept them.
On top of that, Bitcoin has it's blockchain. That blockchain was hard to make. A lot of electricity was spent on it over the years, more then any other coin. This is what makes it most secure. This and the fact that it has been reviewed many times.