Fees in bitcoin are currently and have been sustained at a pretty good multiple of the fees and subsidy several other POW blockchains combined.  Those other chains continue to 'work' to at least the satisfaction of their users.  It may be in the future that security considerations mean that transactions you don't have other reason to trust need to wait for more confirmation.

Traditional banking doesn't settle for days to weeks, so there is an existence proof that current fee levels may be enough and another degree of freedom to offset it if they aren't.  Tools like ecash, channels, etc. have already partially decoupled the speed of transactions from the speed of confirmation.  We should resist falling for it.

Look at the authors of the tweets at the top of the thread, we start with an extreme ethereum shill that has been trashing Bitcoin pretty much since Ethereum existed.  They're just trying to sew discord by convincing people to debate hypotheticals which aren't relevant and may never be relevant.

If there comes a time when fee income isn't significant enough the issue will be easier to consider because the uncertainty will just be about how best to address it rather than also having total uncertainty on the exact situation being addressed.

You're right that there is no guarantees but whatever happens will almost certainly be what the collective users of the system want by the very nature of what bitcoin is and how it works.