re. "all the studies I've seen .. the service life of SSDs is comparable to enterprise HDDs"
Well those studies must be based on SSDs that have been in use for 2/3+ years, which probably means they are SLC or MLC (2 level), not TLC / QLC. Even the manufacturers of TLC / QLC admit their endurance is less, which is why they are targetted at consumers rather than production systems. The other worrying trend is that these short lifespan SSDs are increasingly being integrated into devices, so when they fail the whole device is a write off.
Using voltage levels to cram more data on a comms link doesn't justify doing the same for storage devices. A comms link only has to get the right data once, if an error is detected the data is re-sent. A storage device needs to store the right value indefinitely, if an error is detected, an algorithm must guess what the correct data was.