_Edited to mention Colen:
Go with Colen now, he will help you.
Also, from what I see you are using several AoE attackers but have no debuffer in your lineup except for Tyrum sitting at 1-1. I believe you will find him very useful, you can drop a riposte and defense buffs from the enemy before setting off the AoE attackers, saving the lives of your attackers and also permitting stronger hits. I believe this will make a huge difference for you.
Boril, he tanked for me for ages at 3-60. Good base stats and the Riposte wiped out soooooo many enemy AoE attackers.
Brienne - was said by others above, spectacular. I too still bring her to titans, hand in hand with Wilbur she has a chance to survive against tougher Titans (that for me is just 5* and 6*).
Once I had powerful 5* heroes in my roster I found it incredibly difficult to stay focused on the 3* and 4* heroes but the advice from others in this chain is spot on. Focus on a solid core of a team so that you can win the materials to properly level up the 5* heroes.
Solid 3* team is important for challenge events where completion usually gives you something of value even if you don’t place in the rankings.
Then, solid 4* team (maybe with a 3* like Brienne in there) allows you to complete two levels of the challenge events and more ascension materials and MAYBE complete legendary if the synergies are good.
You’ll want the deeper bench of 3* and 4* for wars as well, it is another good source of materials (usually the war chest has better materials than each war but my alliance has been pleasantly surprised from time to time with the prizes from the wars).
Bane and Valen are useful for a very long time. Carver is good mana controller (I never had him and have a copy sitting forlornly leveling with duplicates only), I’ve fallen in love with mana controllers since getting Hansel and Proteus.
Most importantly of all, have fun.