Miracle and spell damage really dont kick in until 60 faith or int respectively

Most competent opponents in PVP know how to dodge spells, especially lighting spears. Make sure to use Sage Ring as it'll make you much less predictable. If you're comfortable with taking extra damage, Lightning Clutch Ring is also super beneficial. Also, unlike Str and Dex, Faith's soft-cap is at 60 rather than 40.

Just avoid sorcery

I'd love to see someone post a great caster or hybrid build that's totally effective in PVP. In previous soulsborne games I always gravitated toward hybrids, myself, but in DS3 I just haven't found them to be all that great. Really seems like quality builds, maybe only using magic for buffs is the way to go. Either that, or fully commit to a caster type build. Lots of builds can be viable for PVE, and playing whatever is the most fun is usually best, but PVP is another matter. In PVP, you're in direct competition with others, and the goal is to win. Skill will almost always best a great weapon or build, but skill isn't everything, because some things just put you at such a strong disadvantage. I've run across a wide variety of opponents in PVP, but the ones I've faced who appeared to be full hybrids or casters were noticeably easier to beat. Would be awesome to see someone who's found a way to make it work as well as a melee/quality type thing.

Do you have a strength weapons you favor? If so, I recommend just getting the requirements for the weapon and then focusing on getting 40 faith. Also, my friend made a really cool blessed faith build where he's constantly regenerating health. So definitely infuse that weapon. Just upgrade your talisman and you'll be set.