Aside from writing end-to-end test automation, the best SDETs add value in many other ways. They triage bugs, use their deep product understanding (frequently the best on the team) to refine requirements and build test plans, coordinate bug-bashes and large scale releases, measure and report on quality metrics, and much more. All of this takes considerable load off other members of the team (SWEs, PMs, EMs, etc), allows the whole group to ship with much higher confidence, and increases the number of defects caught before making it to production.

If you have an organization where end-to-end tests are easy to write and very quick to execute, then I think the need for QA folks is greatly reduced. In my experience, once there's enough complexity and scale to a product, it's basically impossible to have a rapid TDD loop with enough end-to-end coverage that allows devs to ship features with perfect confidence. Combine that with all the other "hats" QA folks wear, and I think it's is a role that pays dividends in product quality and the efficiency of others across the org.

At the end of the day someone needs to answer a simple question - "Is the product functional right now / after the last release?".

If you don't have QA team you either rely on your product person to "give it a spin" or your engineering who are generally not very excited about clicking through the product multiple times (more often than not, they'll just leave it at the unit test phase and move on).

In small orgs that product person could be your CEO or CTO, meaning this will give them an easy false-escape into "micro-management" mode (aka feeling productive by doing low priority tasks) vs forcing them to make strategic decisions or worse, they'll just block the entire pipeline.

QA creates a natural quality gate looking at the product from the user's perspective, putting pressure at the engineering to deliver quality work and gathering leadership feedback at critical points only.