Your comparison between PC and mainframe computers is not compatible with Bitcoin and any other competitor. Did the dollar become obsolete because a new currency was created? How many companies or governments have considered buying and holding any altcoins. Bitcoin is at a level that will take competitors decades to reach.
The actual
physical paper dollar? Yes, I'd say it's pretty much obsolete today. Today, USD is almost entirely a
measurement mechanism like feet or meters, not an actual technology people use to transact.
And El Salvador is already moving away from Bitcoin and into products that actually work. That didn't take "decades", it's happening right now. And the same goes for thousands of other companies and countries who are trying to solve
actual consumer demand and not just meme speculation.
Bitcoin's days are numbered, and in the world of technology, it's not going to be "slow".