I took the duelist style. And none of the abilities you referenced has anything to do with keeping concentration or avoiding hits or AOEs.
With access to heavy armor plus duelist style your AC is going to be higher then a straight cleric, making you harder to hit in 5e. Though with a breastplate and +2 to dex, you can get an AC comparable to heavy armor. Then add in your +2 ac from duelist your now roughly +4 or +5 higher then Shadowheart is currently on AC, making it more likely she's going to get hit and break concentration.
Your survivablity with stated AC again rough estimate added to a higher overall HP do to increased hd as a fighter, I'll not add in second wind. Your going to last longer as well since your HP is higher, and your AC is significantly higher. Which is also the reason your more of a front liner then Shadowheart could ever dream about being.
Hence the reason I feel your multiclass character isn't a viable option for whats wrong with Shadowheart.
bah forgot to factor in her shield. so figure maybe AC difference is +2 or +3??