@ Nathaniel (no quotes on aeria mobile)
I think the issue with using dgns to level is not necessarily for people preferring to play solo. Some ppl do like to solo ofc, but in my experience, most ppl tend to solo dgns simply for the reason that most of the playerbase does it and they want to keep up. If you are levelling with friends for example, and they all choose to dgn level, would u want to be left behind? Casual players dgn grind to reach the cap without having to spend as much time in game; hardcore players dgn grind to race to the top.
As for me, I agree with you that mmo's are about party play. I personally find dgn grinding to be extremely boring if I'm doing it solo; i'd much rather grind GQs and reps until I pass out. But I still ran manor 8 million times with a bard from 57-60 (w/o slidecasting tho and b4 the BM nerf) so that I could reach 60 faster and run the lvl 60 trials with my guild.
On another note, getting many classes capped can be an important part of post-60 builds, for the certs and CE bonuses. That's mostly a more hardcore player thing though.
And finally, there is the issue of making money in-game. Because sadly, no matter how many reps I do in a day, it wouldn't get me nearly as much money as dgn soloing for a few hours would. EE can be very demanding gear-wise after lvl 60; even sooner for tanks and healers. And getting gear is just expensive :< for some lvl 60+ dgns, if the party isn't geared, be it the tank, healers, or dps, you'll get destroyed. Crafting is expensive and risky, gems cost a ton, and ap items like safety stones and chisels to enhance gear further cost tons. TONS, lol. If players don't buy ap, making that money is harder to do. Sure you can craft or merchant, but even then you need money to start. Dungeon soloing, whether you slidecast or not, is a good way to make that money.
And finally, and sry for the wall of text, but I always have an issue when players say that classes aren't meant to solo non 1P dgns. Forget about slidecasting, I'm not saying that ppl who slidecast should be able to solo. But ppl who DON'T slidecast, and can solo anyway b/c of their gear, have every right to solo whatever the heck they want imo. If a tank is op enough to pull half a dgn without a healer and live, then kudos to him. If a dps, be it a mage, cleric, theif, samurai, ranger, what have you, has the gears to do enough dmg to kill mobs their lvl b4 they get to them, then good for them. I'd say that's an achievement, to be well-geared enough to be able to walk into a dgn of your level and kill the mobs solo b/c you are strong enough to do so WITHOUT resorting to slidecasting. Just my opinion. Maybe it sounds a little elitist, but think of it as me saying that a rich person should be able to buy whatever they want, without resorting to like, a payment plan or something lol (bad analogy but hopefully it makes sense).