I think if you’re targeting developers, SES is your biggest competitor. Their very cheap pay as you go pricing is more attractive than your monthly pricing. If email templates with react is your usp, I think I’ve seen libraries that offer that already.
For example, I maintain a popular email sending library (Nodemailer) and if I could get a penny any time some user files an issue with something that is clearly basic for anyone who has ever even touched email, I would be quite wealthy. All these people are good match for a service like Resend, they just want to send mail for a reasonable price and do not care the slightest of what is going on under the hood.