Weird.
On my experience, cab sims sounded dull, not harsh at first.
Do note - The cab sims sounds pretty much exactly how that amp and cab would sound mic'ed up. This is pretty much how your real amp sounds mic'ed up on stage, but you don't notice because you monitor your real amp directly through the cab on stage.
Anyway, if you don't like the tone, here are some tips:
I'd say, it's mostly in how you set up your amp. Take out presence if it's harsh?
Also, all Ir's are taken with the mic really close to the cab. This makes highs and lows pronounced. There is a built in high and low cut in the cab block. Use it to taste. Sound engineers on stage do this with real cabs too - they cut out lows and highs when mic'ing up a cab.