Apple does have an alternative. The battery issue is neither irreversible nor has any permanent ramifications to the remedy of just replacing the f-ing battery. In fact I have no problem with graceful degradation as a stopgap. Explicit Power Saving modes already do that.
But the issue at hand is completely orthogonal and has to do with why Apple refuses to, at the same time as undervolting, also signal to the user the one sane action to take, which is to obtain a battery replacement. By not signaling such and misdirecting (whether intentional or not), they are passive-aggressively telling the user to replace the entire phone. How else would a typical user interpret this situation? In what way could they know the appropriate action to take from observation? You think a company that prides itself on every meticulous detail of the UX just "missed" this?
Yes it would be great if everyone went to Shenzhen and made their own iPhone from scratch but I’d much rather Apple handle the details for me and my parents and grandparents...
I’m the only one that would be slightly entertained by the harsh realities of batteries being used under duress.
Nobody wants a DVD player which throws up an error and stops playing if the disk is scratched, compared to retrying then skipping on a few frames.
Nobody wants a streaming video which stops playing if there's temporary bandwidth problems instead of pixelating briefly and coming back.
Nobody wants ECC memory or hard disk error correction or parity bits removed and corrupt data to become more common because it's "normal behaviour".
Nobody wants fanless video cards that overheat and break permanently instead of slowing down a bit and staying working.
People do want run-flat tyres because they'd rather keep going instead of getting normal behaviour of hitting something sharp.
People do want sat nav which recalculates the route in the case of "typical operating conditions" of making a wrong turn, covering up the normal behaviour of "giving bad directions from then on" with much more useful behaviour of "giving good directions".