I lol'd.
SPAs are a fad. Apps that rely heavily on REST API and browser rendering rank terribly on Google.
Create a SPA and help your customers discover your competitor on the first page of Google.
SPAs are great if your customers actually want an application. Figma, AirTable, Google Sheets. These don't make sense as server rendered pages.
If you're in the publishing business and need your articles to rank high on Google, then yeah its probably not a good idea.
EDIT: Or Slack for that matter
Generally, when I'm building a business, I prefer not to assume that Google will eventually, at some point in the future, solve the crawling a SPA site problem and finally discover my site.
I'd rather get my 70%-80% organic search traffic today, with any boring server-side rendered tech stack.
Why people use js/spa/etc stuff as the basis for a content/marketing site... I don't know. I mean... yeah, I know why - mostly to expand their skill set. But there's usually no functional benefit, and usually some drawbacks, as you're pointing out.