I am with you on this. I have had 3 Exmark machines and like you said they are great on perfect grass but really drop the ball in less than ideal conditions. What I find funny is that they haven't really done anything to change their product line over the years except 2 things, new lazer and the vantage. Lets not forget that they have had the same walk behind lineup for more than ten years with the only update being a name change and dropping the 32" hydro Viking. The Vantage while nice and relatively new is little more than a Grandstand with a Series 4 deck on it which has been around for several years as well. That leads us to the Next Lazer Z, maybe one of the smoothest, easy to operate mowers I've ever been on. It comes with a great Series 6 deck and leaves a great finish, well unless you are mowing before 10am or the lawn has a few weeds then all you get is clumps and double cutting. As of now the only Exmark/Toro machines I will consider is a 21"/30" mower. I have bought a Scag 52" Vride and don't see myself going back.
Knowledge is knowing a tomato is a fruit, wisdom is not using it in a fruit salad.