A well played Mesmer can do extremely well in PvE. However, the general view is that Mesmers don't work well in PvE, which isn't true at all when the person playing one knows what they're doing. I've got 24 PvE titles maxed on my Mesmer mainly using Heroes & Henchies, WITHOUT the use of ursan, buying runs, leeching, etc. (I don't have Drunkard, Sweet-tooth, or Party Animal titles yet.)
There are two big problems with how people view Mesmers. The first is that many people who have little or no experience with the class don't know how and what exactly it is that Mesmers DO. The other problem is that GW is saturated with a cookie-cutter mentality and people want to get things done as fast as possible. Some of the best things that Mesmers can bring to a party go unnoticed because of the lack of visuals regarding their spells (no flaming rocks falling from the sky). I did THK with a PUG (M & B)and afterwards the party leader PM'd me and said "I don't know what all you were doing, but I've never seen ANYONE running around casting spells as much as you were! Wanna join my guild?"
Rangers are very versatile and can fill many different rolls. BHA gives them excellent interrupting ability. Applying conditions is also something that Rangers can do very well. I don't play mine much, but I don't have too many troubles getting into groups for normal PvE play.
(I hope the OP has enough time to read all that

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