thats not a right answer. Now miners can sustain the difficulty because of block subsidy and bitcoin raising in value as asset. At some point, is expected to be found some sort of equilibrium where the tx-fees need to pay entirely the security of the network. I think if in the next 15-20 years bitcoin would see the same use of today, we can say it has failed someway.

In my opinion also the opposite alarmism, about the "security budget" is bullshit. The only metric to consider is adoption, and adoption, in every form, come always with blockspace demand. If theres adoption, so theres blockspace demand, so no problem for bitcoin in any case, equilibrium will come.