If lights were fast, manoeuvrable, and had a small hitbox but carried few weapons
Mediums were somewhat slower, as manoeuvrable as lights, have a larger hitbox but carry more weapons
Heavies are slower, much harder to turn, have an even larger hitbox and carry even more weapons
While assaults are basically giant crawling turrets...
Then:
Mediums will outgun lights while still being able to hit them all the time, so medium > lights
Heavies will outgun mediums while still being able to hit the mediums because the mediums are slower, so heavies > mediums
Assaults will outgun heavies while being able to hit them of course, so assaults > heavies
And lights can't compare with assaults' firepower but can remain in their blindspot forever, so lights > assaults
While it takes some skill for a medium to stay in an assault's blindspot
Takes some skill for a light to stay in a heavy's blindspot
Takes some skill for an assault to hit a medium trying to run circles around it
And takes some skill for a heavy trying to hit a light trying to run circles around it
At the moment because mediums are too sluggish,
1. Lights can stay in their blindspot half the time, so lights > mediums
2. They can't turn well enough to stay in an assault's blindspot while still firing, so assaults smash mediums' face into the ground
= Every thing > mediums
Therefore, few people pilot mediums (except the Zombiewang, but that's because the 1/4 damage to its central torso because of its hitbox arrangement gives the Zombiewang greater effective survivability than a Stalker).
And while the cicada can reach the speeds lights can, it cannot turn half as well, making a cicada an easy target for any Jenner or even Locust pilot to kill with impunity in a 1v1.