The whole point of Bitcoin is for the participants to not judge what "useful" is. Bitcoin is not designed to be cheap and it's only as expensive as the demand for it. Anyone can take the initiative to enact their own policy so I won't yell too much at that anymore, but decreasing decentralization via usage is not a good argument imo.

The whole point of consensus is to make sensible limits that prevent the crossing of the threshold into being insufficiently decentralized. The agreement to these limits pre-inscriptions indicate we find the growth rate of the blockchain with those parameters acceptable. In more concrete terms, with 525600 minutes in a year, 52560 10-minute intervals, and 4mb for unpruned blocks we'd be agreeing to an approximate max growth-rate of ~210GB per year. So now let's look at the cost for that.

"...there has been an 87.4 percent $/GB decrease since 2009, from $0.114 to just over $0.014."

With around a penny per gigabyte, 210GB is less than 3 dollars a year to support. For pruned nodes the data requirements drop to ~53GB which is even less. Thus I wouldn't say storage costs make the network non-trivially more fragile. The increased bandwidth that comes with large transactions also contribute to the decentralization, but not to an unreasonable extent for most node-runners.