I'm not denying that Spellcasters are good in PvE but only REALLY good late game with the right gear. It takes too many items to get the desired effect from spells. One of the many things that DS2 did right. All you needed was the stats and the catalyst and you were set.
Here half of your inventory needs to be devoted to spell casting for solid results to make it worth sacrificing all that Estus. OH AND DON'T FORGET you also need the Sage Ring unless you have a lot of stats put into Dex since Dexterity affects your casting speed.
So, Attunement, Intelligence, Dexterity, whatever End and little Vigor you have and then two sorcery rings, the sage ring if you don't have good Dex, a good staff, the crown headpiece, the candlestick, the right spells, and a dumb player opponent who will sit there and let you him them with the most telegraphed attacks... and I think you're set for a good Spellcaster PvP build!
Or you know... nearly any Melee weapon with some Vigor, End and Vit and some STR and DEX and you're good for the whole game based on personal skill.
As interesting as it may be to go pure spell caster unless if I'm on my main on my Xbox and decide to be really curious about it... I ain't touching pure spellcasting anytime soon.
I mean yeah a spellcaster can work at times depending on the environment and the scenario but a pure spellcaster in a PvP fight will always ALWAYS lose if the other "normal" build knows what they are doing. Spells are so awfully telegraphed and provide no poise that you're screwed if you get hit/interrupted.