I think your theory seems like it comes from assuming an ENFP can't use Ti and then making sense of the data to prove it, instead of looking at the data and seeing what can be proven based on it. What you say only makes sense if we assume from the get go ENFPs don't use Ti. I'm personally not convinced.
I'd be much more inclined to agree that good use of Ti is a rare occurrence in ENFPs than to say they flat out cannot use Ti, and only use Te.
But regardless of all that, would my ease with logic imply that I'm using Te effectively (i.e. do I have good Te)?