"Variety of powers" is a gameplay thing. You have to separate it from story. Jack fires off and teaches Singularity at Grissom, but she doesn't actually have the power in ME2 or Armax.
Shepard is already a galactic wide celebrity. They're not some mystery person that people haven't analyzed yet. They've been studied in and out by Cerberus. Miranda is a scholar of everything Shepard related and had to genetically reconstruct the personality as well as talents. Their "best biotic" status would be mentioned somewhere, if it really was true.
It isn't just about energy output either. It's control and endurance. Shepard can't even levitate or do the biotic bubble. Like if you take Kaidan to the Ardat Yakshi monestary, both him and Kaidan admit they can't do this. People like Samara and Jack are a different level of biotic talent.
Also, the story of Jack's dossier was added to later where it was Maya Brooks that wrote it. She has firsthand experience watching Jack nearly take down a whole station and scaring the crap out of Kai Leng. It wasn't data all from Pragia. While the War Asset description is just developer jargon. It's about as official as it gets.
It doesn't mean Shepard is worse or losing anything. Shepard is a complete package. A leader. Jack is a specialist.
What's that thing, about those who can't do... 
Variety of powers is not a gameplay only thing. Notice how I didn't reference damage or cooldowns. Those are gameplay things. But if you can do more things, then lore-wise you can do more things.
As for what is or isn't said about Shepard his combat skills are almost never referenced anyway. He's not listed as the best shot, or the best tech power user either. So this doesn't stand out. He's most notable for his leadership and charisma. People like to categorize, and to focus on one thing. That does not exclude other characteristics or achievements.
I don't have an adept Shepard, much less Kaidan alive so I never saw that dialogue. Question is when has Jack levitated? All I've seen her do is raw outbursts of power.
She can hold the bubble in the suicide mission sure. But so can Jacob. The thing is, the latter falters because he doesn't have the strength and endurance. But this does indicate the control needed for that bubble is nothing special, relatively speaking. You need trained biotics to do it, of course. But not superhuman biotics (at least, not if you only need it for a short while. Personally from what I know of the lore only Samara should've been able to do it flawlessly. But that's just opinion. Further speculation: would adept Shepard have been able to hold the bubble? Control we know for sure he's got. But the endurance? Could've been interesting if biotic Shepards were given that as a choice. Or even tech Shepards the choice of going in the vents. How much do you really trust your team? 
"Data from Pragia" refers to useful results from the research used to create Jack, such that they might be theoretically replicated. Battle data would only be marginally useful. As for Jack tearing up a base, we know she can do that. Wild raw bursts of power are indeed her specialty. But again, when has she demonstrated fine control?