I leveled a toon from lvl 3 or 4 all the way to 80 in Orr by joining the karma train, you can still do it now if you so desire but event rewards have been nerfed a lot it seems
I never see the Orr karma trains anymore at all, I think those folks (on my server) moved to the Queensdale or Frostgorge champion trains. You could certainly level with the queensdale champ train as easily as anything, though for myself I can't stand more than 2-3 loops before I just wander off.
I'd say the vast majority of players do their 1-15 zone, then expect to head into the 15-25 zone to continue that races feel. It's not until after that, when you are given the notion that you can/ should go anywhere. There's certainly nothing in game saying "finish this starter zone, then go do another starter zone before advancing further", for a new player to learn. I'm not saying you're wrong in any way, obviously. I think a lot of folks forget to "complete" the capital city and Lions Arch also.
IMO, the game is great for wandering around, leading to such situations where you complete an area and the next area to wander to isn't suitable. It does happen in nearly every RPG that isn't specifically linear though. The only frustrating issue with GW2 for me was the personal quests, where a few of them lead from one directly into another (the vigil comes to mind), but they might be 2-3 levels apart.
I don't disagree at all, I know most people playing would expect to go straight from the level 1-15 Charr/Human/etc zone directly into the level 15-25 zone of the same race... My point was merely that the xp rate if anything is kind of designed to make you go exploring into other race zones, which for map completionists is a non issue, but could use some "hey this area is a bit dangerous for you here, why don't you take the Azura gate and go help out another race to get stronger and come back after some training" NPCs near the entrance of the 15-25 zones to point out hey there are other races areas to try out and they are but a hop skip and a jump away by transportation gates. The lack of explanation of how to hop from one race starter area to another does make it something that most people would not think of doing or know how to do even if they wanted to since the gates are only obvious if you know they are there. Just like some people may also not play lower then their level content because they don't realize that loot dropped can be of their current level even if they are in a zone 30 levels below them.
All in all, your point is valid, my point is just merely allowing the person who posted about the lower then expected XP ways of getting more then enough XP to the point where you are always downscaled because by the time you finish a zone and go into the next your already well above the suggested minimum level.
The lack of explanation of how to hop from one race starter area to another does make it something that most people would not think of doing or know how to do even if they wanted to since the gates are only obvious if you know they are there.
Yeah, the personal quest really doesn't give a very broad view at the start of things. Lots of ways they could have expanded on it. Really though I think they just could have made leveling faster without actually changing the game a whiole lot.
There are some that give 15% though. I've heard that the +10 is actually suppose to be 10%, but it would be hard to believe that they wouldn't update the tooltip even after almost a year and a half.
You obviously don't know how Anet works then. They'll leave shit broken for years, and then maybe, MAYBE admit that it's been broken that whole time....and then still potentially not fix it. There is a ton of stuff that's been broke or not working correctly since BWE1 and still hasn't been fixed. It's pathetic really, but par for the course with Anet.