It's pretty easy for a dev to send emails from Google Sheets using Apps Script. If you want to send bulk, custom emails, then something like MailChimp can do this for free/cheap.
If you're looking to send thousands of emails, then you likely have a large customer base or a big marketing budget and can afford a proper tool.
I mainly use Sheets to automate internal processes, linking to Google Forms. Plus there's free tools out there, for example AutoCrat[0] that can do a similar thing, albeit without the SendGrid/SES link. But then again, if you're aware of SES you're probably technically minded.
I may be wrong though, good luck with it either way. If it doesn't gain traction, open sourcing it with a tip jar may be a nice touch and help keep it alive.
[0] - https://workspace.google.com/marketplace/app/autocrat/539341...