Hmm... In my spy heavy games I found that sending my agents on 78% missions every year results in quicky running out of operatives.
I think your guy is just really lucky. Unless you of course save-load a lot for missions. Anyways, I recently tried to tech-race the cat-guys with Ketaros. In the early game, even yearly steals gave me an edge. Kitties were better, but I surpassed other civilizations.
In the mid-game, I had two agents remaining with 40%+ espionage. They could relably steal techs in 3 months, but they still weren't enough to keep up with the Zenox. As I see, the increasing research-costs of high level techs mitigate the effect of corporate espionage well enough.
All and all, I think nefring espionage would render this asset meaningless for races that has no bonuses on it. Map-stealing is good, but it only saves a few explorers.
I'd also love to see some numbers on how much chance a regular Empire has to raise a 20%+ espionage agent in it's first 20-30 years. Without excessive saving and loading, I usually just lose all of them, even when targetting the dumbest people with the easiest missions.
Why can't I make friends? Only my Nuclear Devastator understands me.