True. It definitely has elements of Detect Thoughts...influencing them instead.Even though the caster is not getting the information, the "magic" of the spell is producing it in the targets mind.
It would not "have to be better than Suggestion"...it would have to be en par with...as they would both be 3rd level spells. You seem to be using "flexibility" as the metric by which spell levels are determined...and while I will grant it can certainly be one element, it is not the only nor even primary one. Things like duration, amount of damage, range and area of effect, the fact that a spell may be a more powerful, or more specific -and thus more powerful- version of a lower level spell can all contribute to what "tier" of magic a spell falls in line with.
This spell, Glib Response, gives you very specific, exactly correct, information...and the target hears it and believes you said it. That is not en par with Audible...oh what was it in 3e?...Ghost Sound! An audial illusion cantrip where it is something inexact, no specific words, unable to determine any more than general direction of where it's coming from. Nor is it 1e's Audible Glamour, a 1st level. Nor 1-3e's Ventriloquism.
The parallel to Detect Thoughts seems a good one to me. The audio component/exact speech of the illusion easily within the power of a 2nd level spell (Magic Mouth anyone?).
I will stick to my assertion it should be 2nd. 3rd is a bit much. You are, of course, free to do what you like. But then, you asked.
