On healer’s perspective, balancing so that newcomer and synced player output remains the same will also be a nightmare.

How do you ensure a sprout WHM in Sastasha with only have Cure I & Medica in their arsenal to match a lv90 who has the following:
• Regen
• Cure II
• Cure III
• Medica II
• Divine Benison
• Asylum
• Assize
• Tetragrammaton
• Solace
• Rapture
• Lilybell
• Benediction

Do you force all GCD heals to heal only at 450p and call it a day? Not quite! Off-GCD heals are not bound by GCD so a synced down WHM can still heal more than the sprout WHM. Are you going to nerf their GCD heals lower than 450p now to compensate that? Or you straight up nerf all oGCD heals to heal nothing at all? And finally! The dreaded percentage based heal that is Benediction! How do you scale that one? Lastly, there are still utilities like Temperance. Sprouts do not have access to that so are we going to nerf Temperance to only mitigate 0.5% damage now?

No. You just can’t, without breaking something.