I think you are onto something with the bookends becoming more severe at the expense of mid winter....and if you think about it, may tend to expand the ceiling for high end events due to increased baroclinicity....lends itself to increased frequency of blockbusters.
Not only are we getting warmer, and injecting more energy into the atmosphere, but as mother nature tries to compensate for that by shearing storms with a greater frequency....the ones that do succeed are more likely to occur early or late in the season, when the compressed flow is less likely to be an issue and potential is already higher relative to the seasonal nadir.