As a note, editing the biomes.xml file is very easy by using any image editor. So you can always just change the biomes after making a map with RWG. If course, you will know where the biomes are since you drew them. You can get around that by making a lot of different biome maps and randomly placing one in the folder of each new map so you don't know what they are anymore.
Or, as mentioned, terrain can make maps for you or even just make a biome map for you if you want to stick to RWG for the rest.
Just keep in mind that changing biomes means your traders aren't in the biomes TFP thinks they should be in. That really isn't a problem, but something to keep in mind. Also, don't change a biome map for a game you are currently playing. Only do it before starting a new save with that map.
And yes, I also feel that RWG isn't random enough. I have up on using it for maps a couple of years ago because it just didn't offer any options and what very random even then. It is good for people who just want a quick map or new people starting the game, or even people who just don't care about the map. But it is definitely very generic for people who like random maps.