.. I've rarely seen WC51 used in late game because they almost never get rebuilt so I don't see the point in removing something that rarely gets used...
How many kubels to you see rebuilt? (or even built...)
When the unit occupied a commander slot one could try to justify it because of it.
Since then it was buffer further and merge with m3:
• WC51: 4 to 3 (pop)
WC-51
-Can now be built from the Rifle Command with a build time of 22.
-MG cooldown duration from 1.25/2 to 1.25/1.5
-MG Rate of fire multiplier from 1/0.8333/0.6667 to 1/1/1
-HMG upgrade cost from 60 to 45
-Veterancy requirement from 360/720/1440 to 300/600/1200
-Can now capture territory; Capture and decapture rate of 1.
-Mark Target and 155mm Artillery barrage range from 50 to 60.
The unit is currently simply OP.