I'd have to agree with Trips, the main issues are speed and low base attack. Accuracy is also low but not sure how high it really needs to be for campaign, probably not very.
Of course, part of the problem is you don't have an amulet nor a banner. You might want to do some runs on spider, even if it's only stage 6-7 or so, until you get at least one amulet. Doesn't even matter for now if it's a good one, anything will be better than nothing.
Secondly, a lot of your pieces are common - honestly, 4 star epic pieces like the ones from login rewards might be better than 5 star common, on the whole, you'd have to compare case by case. If you have crit rate gloves, you should be able to get enough crit rate without needing a set bonus, so you can get a speed set bonus instead.
And last but not least, yes, chapter 8 is bad affinity for Kael - so skip it and try farming higher stages with better affinity. 12.3 has a perfect affinity matchup for Kael and the other starter champions. Though you will indeed need higher speed and attack for it.