1. No, bitcoin is developed by hundreds of actual developers who create amazing features not present anywhere else, while deploying it on a live billion-dollar value blockchain while keeping it secure; most other cryptos are just copies by get-rich-quick kiddies who have no idea what they are doing.
2. That is true; same can be said about IPv4 but it still rides along for 30 years.
3. Oh no, most of the infrastructure already assumes bitcoin, promotes bitcoin, uses bitcoin. Of course, everything can be switched theoretically, but not "trivial", and sometimes even impossible, for example for the hashing network. Which is, regardless of what you say, the greatest strength of bitcoin.
1. Tell me about these unique features that aren't present in any other crypto and that make bitcoin unique.
2. IPv4 didn't have important fundamental flaws that made it impractical.
3. For the users and services it IS trivial to switch to new cryptos. Only smart investments around bitcoin are those investments that go in into the service framework. The beauty of those investments is that they aren't dependent on bitcoin and it's price. Most of the support services earn by volume and if bitcoin fails then it's not hard to just switch cryptos.
In my vocabulary, buying BTC or any other crypto is more of an gamble then an investment because of this.
1. working multi-sig implemented in actual businesses, for one.
2. oh yes it did. it had a 4 million address space problem which was noticed 20 years ago and was fixed in a follow-up protocol ipv6 18 (!!) years ago and still it has 3% penetration regardless of everyone's efforts. Because it costs money to upgrade all the infrastructure! Even though most hardware supports it, nobody cares enough to fix software because there's no fatal flaw and everything "just works" on ipv4. That would be the reasoning why bitcoin, if ever replaced, would go out in a very long co-existence process with a new currency.
3. there is some truth to it, that service investments are currency-agnostic, however as I firmly believe, bitcoin can't possibly just "disappear" as myspace did - many unique services are bitcoin only, millions of USD in support network is bitcoin-only, so the switch will be slow and painful, not matter how amazingly good new currency might be.
Your reasoning is very similar to early delusional bulls who said "ok bitcoin is so much superior to the world's financial system that it will replace all of it tomorrow". This just does not happen like that. Step 1 - you build something that is unique and impossible under the old system. Step 2 - you win users to trust you with their finances. Step 3 - they move.
You think that right after you come up with a better idea you go to Step 1 "it wins". You miss alot of steps.