I can see how for most CN posters, Rosa is rather a GT domestique.
Personally, the first thing that comes to my mind when I think of Diego Rosa is the the long Milan-Sanremo breakaway of 2013, unfortunately broken by RCS's shameless decision to retract a long part of the route, including the Turchino and the Maniè. It's still sticking in my throat.

Those modern orgas have no sense of epic. So you could see Rosa and the other breakaway riders (whose names I forgot but kind strangely, I remember him) starting back from Cogoleto with the lead that they had before the ascent of the Turchino that never happened.
Honestly it was the day I discovered him, in his Androni jersey.
He still did MTB afterwards, though, the Italian nats, I think.