I don't see that one year (and a Covid year, at that)will make any difference at all to his development in the long term, assuming that his heart issues are behind him. He doesn't lose his skill, mind, and once he gets back training his body will recover. He's 20 yo, when things heal up fast, especially for guys like whom who go after it, and seem to pay attention to training and diet more than most.
I always thought that expecting him to contribute last year in the NHL was extremely optimistic. At this point, I am hoping he will be able to be up in 22-23. Boldy took two years to develop, and IMO is a similar level prospect, playing an easier position, with zero health issues and a smoother development path. Don't see how we can expect Rossi to get up faster than him, given all those factors. It's not his problem that we have a shortage of C's, and we shouldn't rush him because of it.