I guess Skyreach runs in a group with a strong DD is still the fastest, but also most boring and repetitive, way to grind up. I personally prefer what Nestor listed, additionally crafting writs and Undaunted pledges give nice XP.

Also note that CPs have heavily diminishing returns now, i.e. the first half of your CP have a much stronger effect than the second half. The need to gind up to maximum is not as prominent anymore, you won't be twice as strong at max CP as at 50%.

It's possible, but it's slow and even more boring than it's for a DPS specced build. I really don't understand why people struggle to grind on dolmens by trying to Pierce Armor everything to death. I would go mad trying to do that (again). I was kinda forced to do overland content specced as tank on my first character because there weren't that many skill points around - IC had just been released - so I couldn't spec medium armor and more offensive skill lines like 2W or 2H because I also had to heavily invest those into crafting. Nowadays if I want to grind a character, which I do usually during the double XP events - also they didn't exist back then and mobs were way under your level - I don DD gear (ex. Medium Armor, bow, daggers) and grind using those.

If you want a grind a skill or skill line you can simply dead-slot them (without equipping the said weapon) and fill the rest of your bar with relevant DPS skills. They will train pretty fast. For example if I want to train 1H+S skill line on a char I would simply equip a sword and shield once to gain it, swap back to daggers, slot Puncture, kill some mobs until I unlock Low Slash, then keep going until I hit 50 and unlock Shield Wall, keep skills on my bar and morph them as they hit rank IV+, then train the morph etc. When I trained my Stamina sorcerer's 1H+S skill I only kept Steel Tornado on the front bar in one slot, then filled the remainder with Pierce Armor, Heroic Slash, Absorb Magic, Invasion and the hard hitters like Hurricane & Endless Hail on back bar. For armor I simply equip 5 pieces of medium or light, then a piece from the other types. As I gain XP, those skill lines train as well. Usually when I hit level 50 I'm at 50 with the main armor line, and at about 38-43 with the others. That way I don't have to gimp myself at all.