I think you're overplaying the "static" card. If you're using the JAMstack the static bit is only half of the equation. Need a contact form? Now you need a form-processing service and it's no longer static. If you're replacing old PHP + MySQL sites you'll need a lot more than a static site generator. "Mostly static" might be more accurate but then how long does that last? Clients typically want WordPress plus a ton of plugins. I don't see how JAMstack addresses that need. You say it's nearly 100% free but I just looked at Netlify's free tier and you're only allowed 100 form submissions per month after which they're $19 each. I don't think I would get a night's sleep with that hanging over my head.