What's your opinion on Debutify, Shoptimized, and similar themes that claim to increase your conversion rate for your Shopify store?

Yes it does. Other premium templates help with that as well. "Debut", "Brooklyn" - everybody is using them and the features on Debutify are quite good (Sticky-Add-To-Cart, personalized pages etc.), so yes - it helps. But it does not if the product stinks or the overall UX etc. doesnt. If shipping still takes 50 days - no.

These themes are not up to date for conversion rate optimization standards. Maybe 2-3+ years ago but in 2020/21 it's a big no. Fake countdown timers, x People are viewing this right now, payment badges below the ATC, countdown timer in cart etc. Everyone knows these are fake including customers.