There are exceptions, e.g., I sent an email full of research with sources to a family member I've been emailing with for fifteen years and it went to spam, despite it being @gmail.com to @gmail.com. In retrospect, I was misusing email versus sending a document or a link to one with it in.
The times have changed. It's not unreasonable to expect how people use email to have changed, ergo people sending emails full of URLs are statistically more often than not spammers.
Is it a broad stroke? Yup. But I'm willing to bet that I'm a fringe case and it prevents a ton of spam.
You can even test it yourself without fancy tools by sending emails full of links and mentioning keywords like Viagra et al.
For other filters/ISPs, content can matter a bit more, but as a general rule for consumer mailbox providers, metrics are the primary thing that affects filter outcomes.