This is right for Google. Worth noting the equation flips for AI search though. ChatGPT and Perplexity don't care about your crawl budget or Core Web Vitals. They cite based on brand mentions, content depth, and whether authoritative sources reference you. So you can have perfect technical SEO and still be invisible to AI-generated answers, or have a mediocre site technically but get cited because you're the known authority in your niche.
Learned this the hard way. Sent maybe 50 outreach emails from the same domain handling transactional stuff (signup confirmations, notifications). Domain reputation tanked within a week and the transactional emails users actually needed started landing in spam.
The painful part is recovery. You can fix SPF/DKIM/DMARC in an hour but domain reputation takes weeks to rebuild. Microsoft's SNDS portal shows you almost nothing useful while you wait.
Set up the subdomain split from day one if you're a small SaaS. Costs nothing.