Yeah, one of the nice things about the believers is: a) You're good at expending and paying less in support than other factions most of the time. b) You are yourself immune to probes - there will ever, at most, be one other faction that that ability, and even though the Data Angels aren't a great faction, "Super Spies" are definitely still a thing.
For the Believers, spies play an important and crucial support role to many effective believer strategies. They help your military by boosting your tech, and provide a gentle touch to cripple an opponents defenses or industry at just the right time. But the believers have other strategies and fallbacks - she's got military momentum but can ALSO play a damn good builder game thanks to her +2 support former army opportunities. Her spies can be incredibly effective, and she can make a few sacrifices to be immune to enemy spies for as long as she needs.
Oddly enough, it's the Morganites that I've seen dominate with a Spy-centric model. Spies don't really benefit much from tech advancement, and are thus cheap for most of the game - but most of what they do takes cash. Morgan has piles and piles of cash. A good morganite player has more than enough cash to be a real, serious threat with spies - there's nothing quite like building a huge army, and then having a single spy snatch the city they are based in out from under you, and suddenly your army is his army. You've also got a good chance to be the first to build the Hunter-Seeker algorithm (which means no one else can), and thus prevent everyone but the believers from having a hard counter to your strategy... and your spies will insure that if the believers become an isssue, you've got the liquid potential to do a hard pivot and beat them with the tech advantage you've almost certainly earned.
The Data Angels get a nice big spy effectiveness bonus... but honestly, that's not enough to make Spies a major force to deal with. Without the ability to produce lots of them more efficiently, without effective alternate-strategy-fallbacks. They are a one-trick pony, and it's a trick where at least one and maybe two hard counters will exist per game.. That is a serious problem. Their only other ability is "not to fall behind TOO badly" which doesn't even synergize well with their gimmick!
The Data Angels aren't really sucky because they are good with spies... it's mostly because they arguably aren't even good with spies, they are just worse with everything else.