As a game designer, there are in fact good and bad reasons to reroll from a game design perspective, assuming as a game designer you have any sort of design goals whatsoever. For example, if people are rerolling because they've lost interest in continuing to play the game with an alt, or feel the earlier parts of the game are more interesting, that suggests a failure for anyone who wants to make a game entertaining at every level.
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For those that can't shift perspectives to that of the game designer or implementer rather than the player, I would recommend staying away from developer diaries. Designers and implementers engineer things with intent and purpose. You can get lucky and discover that they those things are even more useful in other contexts, but no good designer relies on luck or takes credit for luck. When players find alternate uses for the things you design, you can acknowledge the fortune involved with that while also realizing it still represents a failing on your part when the original intent and purpose is discarded. Its easy from the outside for players to believe that it should be solely up to them to decide how a game is played, but no designer who leaves their work up to chance will succeed in the long run. Ultimately, they will fail miserably and edit themselves out of the genetic pool of the design community.
Those who simply refused to acknowledge that the devs not only could but must have a purposeful intent to their work, those who thought that "vision" was a curse word, lets just say were consistently less successful at doing so than the rest.
I studied both design communication and also rhetoric quite a bit in my undergrad Professional/Technical Writing degree, and my original Thesis for my Masters in Professional Writing was specifically on design decisions in an MMO (relating to communication and new user experiences).
I have no problem at all recognizing that designers and players often have different, sometimes opposing, goals. That being said, in Matt's article his rhetoric clearly implies a very -strong- feeling of dissatisfaction with the desire to create alternate characters in CoH users. It goes even farther, at times, than dissatisfaction into outright disapproval.
Look at your example of a "failure" or "bad" reason to roll and alt from a design perspective. It closely alligns to one of Matt's: the desire by a player to reroll "because they've lost interest in continuing to play the game with an alt." This makes very little sense, from a design standpoint. It suggests that every player's experience, regardless of archetype choice, powerset choice, etc. be exactly similar. That's the only way, from a design standpoint, you could hope to prevent human users from ever desiring to try another "choice." Yet if that were the case there would be no need for archetypes or power variety in game in the first place. Simply make all changes cosmetic and be done with it, So there's never any reason for a user to wonder what the game is like from another set of choices. That, or allow every single player to have every single option on every single toon in the first place. The second option is actually the one Matt mentions admiring in Rift's design. It was also the design intention behind The Secret World.
If your goal IS to allow players to experience different playstyles and experiences, then by nature your goal ALSO includes the desire for each playstyle or experience to have benefits and uniqueness. In a system like that, where the design decision included "differences", then the eventual satisfaction with achievement in one experience or playstyle naturally lends itself to desire experiencing others, as well. That's simply recognizing human behavior in your design choices, and is a direct result of your intended goals.
I would argue that the reason that alts were so prevalent in CoH is precisely because the Devs had such a strong desire, from launch on (I know beta was different) to make sure that the game offered an incredible amount of variety beyond just its amazing cosmetic variation, and each one offered something worth experiencing. This WAS the intended design. I think that has been obvious since launch, demonstrated in the decisions to allow multiple character slots at launch, the continuous launch of new power sets which could only be experienced via rolling entirely new characters, and even with the launch of Epic and Heroic Archetypes, which actually REWARDED you for achieving a certain level with an unlocked alt you would actually need to reroll to experience. Enticing players to want to roll alts was a key part of the design of City of Heroes from at LEAST launch on, not some side effect of a mistake on the devs' part.
Regardless. my point was that it's entirely understandable that many players took his article to mean he didn't like Alts, and thought a good MMO would really have little to no need for them, given both his rhetorical structure and diction in that article. Maybe it was just poorly written and wasn't what was intended, but to pin that on the readers instead of the writer is....misguided.