I think the quoted part is quite telling. I think you are subconsciously applying a lot of extra pressure to make up for the difference in weight between the two razors.
Even if the R89 were more aggressive (and I don't think it is; I consider it to be fairly mild) you shouldn't automatically get a bad case of razor burn as a result.
Razor burn is the result of a bad angle and/or too much pressure.
I think you are onto something, I am applying more pressure to it since I know that it just doesn't have the heft to cut it, I might have to find a heavier handle for it.
What are the weights of R89 and EJ?