AWS UX isn't bad because engineers are bad at UX. It's because inside AWS it's every man for himself, and every team for itself. They don't collaborate, they don't talk, they compete to ship everything as quickly and cheaply as possible - quality, usability, and common sense be damned.
That's not just AWS. That's Amazon generally. All Amazon orgs I've worked for have been like this, and due to the nature of my work, I (and my teams) have been treated like pariahs for daring to suggest that there ought to be even a minimal amount collaboration, shared standards, and cross-pollination on ideas between teams.
Conways Law https://en.wikipedia.org/wiki/Conway%27s_law
AWS UX is bad because there are too many products and features, but also still supported legacy.
FWIW, my team in AWS had help from UI designers who were cool people that impressed me with their work. We definitely had to push through some needless organizational friction, e.g., they were in a different org and frequently got left out of meetings, whereas we should really have been acting as one team. I don't think we saw it as everyone for themselves, we really tried to make it work and had a good, trusting relationship.
In the end, our leadership changed what we were building so often that all of the UI work was scrapped long before we shipped. We ended up launching a janky console, quickly assembled by SDEs who were racing against deadlines. We skipped virtually all operational readiness work to meet the launch deadline. After claiming the launch win, the director, two managers, and the pm promptly left for other orgs.