Hello spark36,
My experience has been that WordPress sending emails directly tends to work ok for low volume. Delivery time can be long (deferred cron jobs waiting for site traffic) and overall deliverability to user inbox (rather than their spam folder) can be inconsistent under some mixtures of circumstances related to email volume, host parameters, sending speed, IP address being spam listed, etc.
We use SendGrid for all transactional emails on 100 plus sites and also for mass newletter emailing to 40k plus recipients. Transactional emails are received instantly (password rests, etc.) and we have very few reports of Newletter delivery hitting user spam folders.
Even though we run a dedicated server, before we began using SendGrid, we had many user reports of not receiving password reset emails, not receive newsletters, etc.
We no longer get such reports with SendGrid.
This article may be of use:
https://www.wpbeginner.com/opinion/why-you-should-never-use-wordpress-to-send-newsletter-emails/
Best of luck!