I haven't been able to get the Kaidan Biotic Shepard dialogue, not for lack of trying. But I think when Kaidan talks about biotic spikes, it might be important to remember that, at the time of it going into record, he was probably holding back and/or out of practice. It's only after Eden Prime that he's "not holding back anymore" and suddenly starts to grow (apparently exponentially) in terms of biotic power. I think he hasn't hit his potential yet.
And when they talk about him being as powerful as an asari (which is variable - some asari aren't good biotics), they specifically mention him as being as powerful as an asari
commando, for whatever difference it's worth.
So, while I can see him as being less powerful than an Adept Shepard or a Biotic Shepard who has more practice at the start of the game, I think he might eventually surpass that.
But then I play a soldier Shepard. There, it doesn't come up (since the romance is involved and she is not an adept, I guess? Or I haven't been lucky), so he might well be the most powerful human biotic known (up until ME2, where apparently human biotics are no longer rare and lack the same amount of stigma).
Anyway, there's my early morning biotic Kaidan rambling. Have a biotic!Kaidan:

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