I suspect you're going to get some wild variations on opinions as to whether RM is high or low magic. I hear that it's high magic more than I hear that it's low magic. Personally, I find it to be neither - it's just a matter of your groups style and what the GM allows.
Indeed I will. But, I am just the messenger. Most of us have been playing ICE games for a long time and have customized it and house-ruled the areas required for our games. I guess when I see a request for feedback from an Author I want to give it based on the face-value of how the work reads. For a new player- Shadow World reads High Magic. For a new reader Rolemaster reads Low-Magic.
As note the RM reading like Low-Magic is largely due to the Spell Classes (Type I-III) and lack of "attack" spells. Lets face it- its a game and you want to be cool right away.
In my opinion the partnering of SW & RM would be well served by an official adaptation of the RM spell casting system to reflect SW. I think the SW material as written is interesting, and different than any other setting out there- but the aspects of it that make it interesting are largely unavailable to PCs...so, find a way to bridge that gap a little so that players from levels 1-10 can become involved in these interesting aspects that define SW. My observation is that Magic is a gap that needs to be bridged.
I am not of the opinion that starting at higher levels is a solution. I'm an "its the journey, not the destination" kinda GM...I want players to struggle through the first couple of levels and get a feel for the tone of SW.
Aside from magic, I also mentioned that the multitude of races/cultures is too much to navigate for players, and that I end up pairing the setting down to a bare-bones setting. I assume that this is a fairly common practice as well; but, felt I should mention it as building a feeling of continuity in games is very important. I realise that much of the SW material was written under license and so wasn't under Terry's watchful eye...but, it still exists and throws sneaky curve balls for those of use still running games in 2014! I also think creating a canon list (if it does not already exist) and a GMs guide similar to the players guide would be really helpfull.