As a longtime fellow Tull fan (on them since '68's "This Was" release--I was 13; and, I've seen them about 1/2-dozen times, mostly in the early-'70s), my dos centavos: Generally speaking, Tull has always been Ian's baby, from not only a PR standpoint (silhouette of him playing flute), but musically. If, literally, every living track was written by him (and I haven't checked to verify), Ian can be Tull a little more (if not a lot more) than a gaggle of cats who used to be Tull, and now tour sans Ian, IMO.
I saw Ian in a little club in Austin, TX just shy of a decade ago, and I'm pretty sure he wasn't billed as "Jethro Tull" (but, I can't recall)..."Ian Anderson of Jethro Tull"? More probable.
As Eddie Trunk has always said, make sure you know who'll be on stage when you buy your ticket. That should be the end of it. We can debate, all day, this, that, and the other regarding "artistic merits"....but, as we're decades, now, into the "rock era," we shoulda seen this day coming, at least to some degree, with EVERY band/act/artist. Be aware, consumer....period.