I solved this particular problem by cutting the arms off my steamer

Sure, I put up with arm pump for about a year as I couldn't bring myself to cut up my nice steamer but in the end one day I could take it no more and simply cut them off just above the elbow. Perfect.
There is an alternate solution and that's to buy a windsurfing specific steamer. Most of these either already have short sleeve arms or have larger diameter arms/different materials so they are not as tight. The Neilpryde ones are supposed to be good, however I don't have one myself so couldn't comment definitively.