"Fuel efficiency on an ICE can drop up to 30% after 10 years"

Complete nonsense. Every 15+ year old ICE car I've known or owned was within 5% to 10% of original fuel economy, the reliable brands actually maintained their original fuel economy or surpassed it as fuel economy improves as engine wear in completes at the 20k-40k mile mark.

If your ICE car dropped by 30% then share the brand and your maintenance history.