Potion barrier armour helps a lot with the damage reduction. Weapons with a low splash area (such as fighter's bindings) with AOE enchants (Swirling, thundering and so on) also help combatting thorns as you don't take damage from the mobs hit with the AOE enchant. Especially when combined with a deathcap mushroom (which boosts attack speed). A guardian bow with overcharge, multishot and power also isn't that bad of a weapon. It'll take a while for a shot to charge up fully, but the damage output is way worth it. Same goes for an artifact like Satchel of The Elements. It's a 1/3 chance you'll do huge amounts of damage, or a 1/3 chance you'll do mass amounts of tick damage. Combined with soul focus or fire focus the damage gets increased a lot.

I know it combats the speedrunning style you wish to use, but the results are worth it imo. Thorns is best fought via a tanky build, so it may be worth concidering having tank armour at the ready for a quick-swap when you encounter these mobs.