Well I cussed the shallow deck on my Troy built for a year , then decided to change blades (one of them was bent and cutting circles in the ground) both blades were put on the mower upside down when I bought it at Lowes. With new right-side-up mulching bladed it cuts up a storm.
It looks to me that you are trying to cut too big a swarth, and cutting too low, at too fast a drive speed and a too slow deck speed on too wet to mow turf. Other than that I don't know. The bar isn't the problem, it keeps the deck from bending, nor is the deflector chute, It is mostly the person doing the mowing,..... unless the mower isn't capable of developing full RPMs , then the person doing the mowing should find out why?.