Oncidium just stops growing

[Lagoon]

Ken, In Your photo, the 'chids doesn't appear to be over potted to me. Some real juicy roots there

I've learned my lesson with overpotting - Mold and fungus and the bottom of the pots. I found it very difficult to gain the correct moisture level with much success.
Perhaps the more gutsy growers can or should be over potted to avoid root disturbance.
My wild warrior was over potted and has done very well and bloomed.