It would not be "convulsed". It would be as easy as using wBTC tokens on Ethereum, and can be made as easy as simple Bitcoin transactions, because in the ideal case if you don't need the mainchain you can onboard on the sidechain and stay there. User experience would be much simpler than Lightning's current one.

In addition you could ask the contrary: why does the whole world (full nodes) needs to validate and store every $5 VPS payment? (to not always use the "coffee" analogy )

If Monero was used as much as Bitcoin is now, then eventually it would run into the same dilemma: node centralization (with lower censorshop resistance) or high fees. It has a dynamic block size, so it roughly follows the BCH/BSV model (with a few more restrictions if I remember correctly). This means that in the case of an usage boost XMR's node count could lower considerably if the CPU/RAM costs for nodes to validate transactions explode.

I like and also use Monero, but I also like to have choices, why should I adhere to a monoculture? Not every transaction needs to be as private as a XMR transaction. And Bitcoin has several advantages: simple transactions are smaller, and the Script language allows L2s like Lightning and sidechains and some other use cases, which afaik are not possible in this way on Monero.

That Lightning is stagnating currently is true, it could be related to the attacks discovered last year, but as a "prepaid-card"-like tool for small payments it works quite good as these attacks would never be profitable to steal low amounts, and usability can always be improved.