Common misconception regarding mana potions vs mana regen
I see alot of people treating mana regen as the superior option throughout the entire game. This...is only half-true.
Mana regen is the superior option ONLY for pre-hardmode. You dont have a lot of mana and good mana pots. Coupled with the fact post-skeletron weapons (including Demon Scythe) are not mana effecient and burn through mana, you can see why one should rely on a mana regen build pre-hardmode.
Hardmode is where things take a 180°. You gain access to MUCH better mana pots as well as getting an increase in max mana. Mana weapons this stage are also much more mana effecient and don't devour alot of mana. Meteor Staff is probably the only weapon pre-moonlord that's affected badly by Mana pots.
Someone else did deep testing on this matter. Here is the link to their work: https://forums.terraria.org/index.php?threads/mana-guide.105638/