For surgery, I can definitely see why the RLE is seriously important. It's a necessary step to separate fantasy from reality. Otherwise, there would be quite a few people who would do it on a whim, suddenly realize that the reality is WAY different from the fantasy, and realize that they made a terrible mistake too late.
In regards to HRT, though... well, let's just say that if RLE was required before that, I would NEVER have transitioned in the first place. It took me a good two and a half months of hormones before I finally felt comfortable enough with myself to go out in public as a girl for the first time. If RLE was required first, basically exposing an unpassable person to a world of stares and snickers, I NEVER would have been able to do it. Hell, I only started HRT in the first place because it was so easy to get started on. I wasn't 100% sure that I even was transsexual when I started. I just had hunches, and personal stories to compare to others who had made the jump successfully, to go off of. Hormones were the thing that sealed the deal for me. Suddenly, it was like the whole world just lit up in an unbelievable fireworks display, and suddenly everything made sense, and suddenly for the first time I felt that "sense of self," and that feeling that the thoughts in my head were finally right, and I finally knew for 100% sure that I really was transsexual, and really did want to transition fully. I didn't know before that. And so now because I was indeed able to have such open access to HRT meds, I have now gone the official route, and gone to therapy, and gone to official medical supervision, and am now completely 100% sure of who I am. Before doing my little "trial," I did not know, nor do I even think it would have been possible for me to know.
One of the good things about hormones, is that the mental effects begin appearing very quickly, and yet none of the changes really start becoming permanent until about the 2-3 month mark. So there is a BIG buffer zone in the middle where those who have made a mistake can realize that they have made a mistake, and go off of them with pretty much no permanent damage done. Unlike surgery, where once it's happened, that's it. There is no chance for second-guessing, and no chance to be unsure about it, because once it's done it's done, and you're going to spend the rest of your life unhappy if it was a mistake. So making sure that someone is a prime candidate for surgery, and various "gatekeeping" procedures, are VERY important. Hormones, not so much. If someone's transsexual desires suddenly vanish after starting hormones, and they realize it's not what they wanted, so be it. They stop taking them, go on with their lives, and no harm done. If the same thing were to happen after SRS, though, tough luck. You're stuck with it. You're never going to have your original body back no matter what.
That's my opinion at least. And again, I'm probably biased because I DEFINITELY did not do a RLE prior to beginning hormones, and I'm frankly glad that I didn't have to. It would have discouraged me more than anything, and I might never have found my true self.