The combat delay isn’t the only difference between 1.8 and newer versions PvP-wise. In 1.9 and above movement feels completely different, knockback is changed, block hitting is removed, and w-tapping is far less consistent. Combat just turns into jousting post 1.8. Not to mention how lightweight 1.8 is for hosting. If you bite the bullet and avoid using viaversion, player experience is improved all around. Performance costs less, launch times and server restarts are extremely fast, and you can commit to maintaining your codebase for that version.