I got some Rainbow Marcellas last year and they were not vigorous at all. Now it looks like they died over the winter. Are they just a weak variety? I had Magnus, which I started from seed, and Lakota Fire, both of which do fine in the same area of my garden.

For me Lakota Fire was a weak grower. I am in zone 6b and none of my Echinacea have started yet , I would give them some time yet.