It's tough to say who was more valuable, or more important, to the Suns success during the Nash years but the Suns made the playoffs while Amare missed the entire season, save 3 games, but they missed the playoffs in the first full season after trading Marion away.
I know coaching comes into play some as well with the year they missed the playoffs being the year they tried the Terry Porter experiment but that team sorely missed the little things that Marion did. Grant Hill did his best to fill in for Marion but that is when people really saw what Marion did. He wasn't a true star but he was the best role player in the league for 5-6 years and that got him a few All-Star nods, similar to how Draymond has been awarded for being the top role player the last few seasons recently.
Would I rather start a team with Amare or Marion? Amare, without much thought but if I had a title contender and was able to add either Marion or Amare? Marion, without much thought. They brought different things to the table and had very different skillsets.
Both belong in the ROH and I expect we'll see one of the two get in when things return to normal-ish and the renovations are done. It does make some sense to hold off on something like a ROH induction to coincide with the arena reopening and celebrating it's renovation. Of course the Corona Virus adds another level to that but from a marketing standpoint, holding off the last year or two makes sense because they were trying to get that renovation approved. Having a sellout for that induction makes it more apparent fans will come when something worth watching is taking place but Sarver sold things as fans didn't want to come out because the arena sucked.