I would agree cyborg had the highest potential ceiling in terms of power, but is also relatively easy to neutralize, especially given defuse.
I also think that very few people bothered to to invest deeply in the Cyborg becauseit was much less glamorous than Marine and Recon, and is commonly perceived to have a lower skill ceiling.
So a lot of people assume the birth is just the worst player of the starting O. Which isn't true obviously.
I think the gap between good borgs and great borgs opens up towards the later years of the mod, when the overall reduction in pings begins to warp the effectiveness of hitscan weapons that are balanced with higher pings in mind (ie mega, and especially SSG)