Your theme won't make or break your SEO. Unless, that is, if you don't go out of your way to pick some obscure one that has no traction and no solid support community. Divi is fine. We use it in just about all of our projects. But using the theme alone doesn't solve the SEO issue. Granted, it doesn't create extra SEO problems, but using the theme alone won't make your site rank on top of Google. I hear this conversation over and over again that one theme is this or that. If you don't set it up properly, and don't use proper speed, SEO, security settings, you won't have a fast, secure, top taking website. Period. In the past few years my team has migrated dozens of sites, with over 100. 000 pages total. These sites generate over 1m pageviews per month. We've had custom themes load ridiculously slow. We've had Divi load ridiculously slow. We even had a case of Genesis theme website loading for over 17 seconds off of a vps. It's not the tools. It's how you use them. If you like Divi because it's easy to use, go for it. it's a solid platform. But don't forget that there's a set of tweaks to make it run fast, that aren't built in because the theme out of the box is set for flexibility, not speed. And that goes for any other theme out there. Hope this helps.