I wasn't aware bosses dropped chests, but can those chests contain interesting or otherwise unique loot, or is it just a handful of yellows/exotics with generic skins?
Just for an example: a single AC path gives 60 Tears for each path, per day, with diminishing returns after that. An AC helm is 180 Tears. So doing all three paths, about 7 to 20 minutes per path depending on group, in one day, gives you one piece of armour. The shoulder, chest, and pants are more (210, 330, 300), so those do take longer. But it still means that on average, doing all three paths once a day is a steady pace to get the armour. But you'd only do that for the looks anyway, since it's quicker to just buy Karma armour from the Temples.
Every main dungeon boss has a chance at dropping unique and themed items only they have, although those items aren't all that great anymore - they used to be, since they were account-bound exotics, but recent changes have kind of lessened their coolness. The early dungeons were mostly backpieces anyway, so they weren't a 'visible' cool item, but they were nice to have as a kind of heirloom since they were account-bound on equip, not soulbound.
But you always come out of dungeons with money and resources (materials), which in turn can be converted into usable weapons and armour quite easily, so I don't see it as coming out of a dungeon with nothing to show.
I do agree though, the Arah set is really only for people who want to punish themselves, or you just buy the runs. Most people charge 5g per run. I'm neither here nor there on buying completed Arah runs.
Even with all those boosts I'm not convinced you can get from 1 to 40 in 4 hours. One level every six minutes?
Granted, I probably also have a fair bit of XP boost from the account-wide XP boost Achievement Points give, but yeah. Perhaps I got lucky with some perfect storms, lots of nice kill-streak heavy events as I explored. To be safe, double that number for a more general "Average". I think 8 hours to get to 40 is pretty reasonable, though I still say people can do it much faster if they don't faff about. Not that I think people should rush it. There's zero reason to rush to 80.
EDIT: Some additional info:
Improved Experience Booster + 100%
Killstreak Booster + 100%
Laureate Booster + 30%
Guild Experience Banner + 5%
Guild Bonus + 5%
Food + 15%
Utility + 10%
Achivement + 3% per 2500AP
So assuming an AP of 5k, you're already looking at, roughly, a 271% bonus to per-kill XP, almost three times the normal rate, not even counting the Bonus from enemies that haven't been killed for a while. The first 15 levels also used a boosted XP curve to make them go faster than 15-onwards, and the whole thing plateaus around 30 so you're always getting 8% towards your next level for each Renown Heart. So if you do 10 Renown Hearts, that's practically a full level (since you'd be killing things while doing them, filling out the other 2%).
This also ignores the possible +10% you can get if your server is doing well in WvW, and a whole bunch of other things I'm likely forgetting. But boosts aside, the most important thing is doing Hearts and Events, really, and staying in zones close to your level.