I hate to say it, but I disagree with Trips completely.
This is probably one of those very few moments in forum history where I disagree.
You should be doing campaign and nothing else.
You should be using the gear you get from campaign to improve your hero.
The pieces you need to improve are the bottom row.
The pieces on the top row are perfect for your currect situation.
Gloves - Chest - Shoes - Need to be higher Star lvl.
The Rarity of the item doesn't matter as much as the Star lvl when dealing with the bottom row
You need to get the highest Star lvl you can get on those bottom 3 pieces.
I have to disagree and take Trip's side here.
The difference of 4* boots to 5* boots on lvl 16 is five speed. You could say that the 5* boots get better substats, but that argument isn't convincing if you give the advice to use uncommen gear from campaign instead of epic artifacts with fantastic substat rolls. I don't see any artifact from campaign will be better than the stuff the OP is using right now. A green 5* armor from campaign may have 10% more attack as mainstat, but it probably will not have the good substats of the actual chest. 10% atk vs. 8 speed, 8% hp and 9 critrate.
5 speed will make a big difference on arena speed boosters later on, but not on Kael at day 7 or so, where the thread OP is right now. There is no need to replace the actual gear with uncommen stuff from campaign, that would have to be rolled to lvl 12 for a ton of silver. Replace the actual gear when you have 6* epics from the Dragon.