In Telepath's own words, slushwave is characterized by the usage of both phaser and delay to achieve the effect of a sample layering over itself, owing its origins to dub. That's it, it's simply a production style.
Besides Virtual Dream Plaza, much of Telepath's work could hardly be considered ambient. Many of his tracks are bright, busy, and upbeat.
Slushwave isn't "vaporwave but ambient", it's defined specifically by the audio techniques employed and prescribes nothing about its sonic characteristics. So why is ambient-focused slushwave considered the "default" for the genre?