If you want to keep preferring what the publishers wanted over what Mendelssohn wanted, that’s your business, but given that part of this conversation has been about how composers decide what to call a piece, I would have thought it was highly relevant to point out that Mendelssohn didn’t call it a symphony.
Be careful what you wish for. Mendelssohn didn't want his "5th symphony" (the "Reformation symphony") to be published at all...
My recording of Lobgesang (Spering) "Symphony No. 2" on the spine "Symphonie Lobgesang" on the title, "Lobgesang eine Symphonie-Cantate Nr. 2" on the back (the Nr. 2 does not really make sense here because there is no earlier numbere Symphony cantata). So they apparently could not decide (and the booklet is a mess with several empty pages, apparently a mistake but the pages I described seem regular).
I don't care either way in which volume Lobgesang is edited or how it is called. But I think it is not very helpful to think that whether it is a symphony or a cantata (or something else) could simply or decisively be settled by what's on a title page, regardless of whether the composer or the editor is responsible. In either case it would be a quite unusual exemplar of its kind and while there is an obvious precedent of a choral symphony with three instrumental movements before the vocal parts and this fact was probably relevant for the publisher's/editors decisions until the day before yesterday, I am not aware of a cantata with three symphony movements at the beginning although many baroque cantatas do start with a short sinfonia which was certainly known to Mendelssohn and might have been
