Right now you can use bitcoin's network effects to some degree with altcoins. eg. You use xmr.to to buy anything that you can buy with bitcoin with Monero.
This is a band-aid of sorts for the time being but I don't see why services that currently allow you to use bitcoin could not upgrade to include a better currency/currencies?
Because of that, the largest cryptocurrencies with the most work behind them will naturally be the most secure the quickest.
Monero might have some very good benefits, but the much smaller size of the network means it's a magnitude easier to attack from a state level adversary.
And the fact that Bitcoin can (and will) evolve over time means that the benefits from other cryptocurrencies can be put into Bitcoin as they become useful or proven.
This is already happening with Bitcoin, and it's not going to stop.
That being said, I don't think that other cryptocurrencies are pointless, and I do believe that they can continue to happily coexist. Ethereum is focused on the "smart contract" side of things. Monero is focused on privacy. They can all have their uses and specializations, and they can all exist together in the same ecosystem.
Even if Bitcoin ends up not being able to adapt and evolve for whatever reason, being a "store of value", your cryptocurrency savings account, is still a valid use case, and can continue to be one even if there are cryptocurrencies that do everything else objectively better.
BTC is going to die to a gen 3 VM that learns from the ETH mess of gen 2 and just ungimps the BTC VM.
I don't believe BTC has the political leadership to fix that poor decision, given that a) they've demonstrated poor leadership until now and b) some of the people involved in the gimping are still in positions of influence.
I can't find a single reference on them that contains actual details on the computational model because the internet is full of vapid circular search bait, particularly about cryptocurrencies.
The last I checked, the BTC VM disabled most useful opcodes, which meant you couldn't actually make money automatically redeemable for a large number of constraints you would want to impose.
My quick search seems to support that the VM still disables many opcodes: https://en.bitcoin.it/wiki/Script
What specifically would you like to see done with Bitcoin scripts that can't be done?
For various reasons, you probably want to use arithmetic and string operations for encoding certain problens. You could do it in bit operations, but efficiency.
I can't take credit for it -- it's one of those things that was floating around as a usage early on, but the features were killed.