Trouble with spellcasting classes and their save DCs in Pathfinder

So I’ve played a caster in several Pathfinder games with my friends over the years, but I’ve continued to have the same problem with a lot of them. Namely, because of how save DCs work and how a lot of creatures are stated, it often feels pointless to use most spells on my list because FORT and WILL mods are always so high that I’d have to hope for 1 on the die half of the time. Even DEX saves can be remarkably high on an enemy’s side so my only recourse is touch attacks or spells without DCs and even then I’ve dumped everything into my casting stat to even hope to make my save DC high enough to force a spell through.

The system is very content-dense, but so far I’ve only managed to find some small buffs like Spell Focus feats to bump up DCs. I think Arcanists have some exploits that can help too but I am currently playing a witch and my options feel rather limited. But it seems like there must be other options out there since so many people swear by casters’ abilities and I know that to be true of this system and others, especially as I’ve seen other friends power game other builds. In particular, my friend’s (current GM) previous oracle build was untouchably powerful. Is there just something that I am missing to make my caster viable? Able to land a spell on a creature with decent saves?