He's not so bad once you get to know how. I think it's maybe intimidation more than anything, that seems to be how it is for a lot of bullet hell-y stuff.
Most of his attacks are able to be
streamed, if you're familiar with bullet hell terminology - that is, they're aimed at you, so you can basically just slowly inch along to dodge the stuff coming at you, while everything else is just kinda there to make you panic by filling the screen up. I slide to the bottom of the box and then inch up for those. When you hit the top is the tricky part, and you have to dodge until you can start streaming again.
https://youtu.be/WB_jJfjfzbo?t=53 video about streaming!
The carousel, devilsknife, and the spade spiral thing aren't streamable though. My personal strategy was to find somewhere and just ignore the big pattern and try to focus on my little area for dodging - so for devilsknife, say, I'd go to a corner and just slide up and down along the wall as the scythes fly in and out. It mmmostly worked. Carousel you head for the right and just move up and down with the pattern I think.
Devilsknife hit's rrreal goddamn hard though yeah, having everyone defend when that attack is coming is probably not a bad idea.
Finally, it helps if you know how Pirouette works, as it's not actually random, so once you know how to use it, you can avoid it when it does bad stuff and use it when it does good stuff, to give you more of an edge. I felt kinda cheaty for using that bit of knowledge, but details can be found here.
https://www.reddit.com/r/Undertale/comments/9t05sv/finally_managed_to_spare_jevil/e8wpfpt/Finally as far as I understand you can't actually gain EXP, and it didn't look like damage was much faster than the other method, so the violent approach is arguably not that much easier - perhaps even more difficult, since you won't be defending to boost your TP, and will probably be spending it on Rude Busters instead of Heal Prayers.