Psychological explanation for the success of "class systems" in video games
There are many explanations and counter examples for this phenomenon. Perhaps I can provide my two cents.
According to Kendrick et al pyramid, an updated pyramid of need, Status/Esteem seems to be reasonably applied to the class systems. Such systems allow the players to practice mastery, in other words, the need to feel competence. This is similar to your understanding of &quot;specialize themselves to feel special&quot;.

For example, two players of healer/damage class may compare HPS/DPS
(Healing per second / Damage per second ) to see who is more
competent. Tanks see who understand the mechanics of the fight more
thoroughly. At this point, the goal shifts from defeating the boss to climbing the highest in the HPS/DPS meter. (this is similar to many sports, where players play for the stats).  This example applies to &quot;World of Warcraft&quot;, one of the earliest MMORPG that introduces the triangle system (tank, healer, damage). The class system provides a measure within the group.
Another example would be &quot;Guild Wars 2&quot;, a game that has no class
system. Players heal, attack, and tank on their own even in a group
setting. The game is a relatively much relaxing game in comparison
with World of Warcraft, which has many hard core gamers.

There are way many other possible explanations on this aspect, but it might be hard to examine specific reasons because there is too much variation in the individuals.