Perhaps they've cloned him because he was so busy.  It did appear to be a list of staff.

However. "Decisions on interpretation" wouldn't have been an issue at all in the 18th century because there'd have been no discussion as to what "18th century style" would have been. So that's one function the armwaver might have nowadays, apart from armwaving. Mr Hogwood is of the opinion that Haydn didn't use a keyboard continuo for his Esterhazy symphonies, although his recorded performance don't make a particularly good case for leaving it out in my opinion. As I'm sure you know, the inflated string sections of otherwise HI performances of (for example) early Haydn have more to do with the kind of spaces they're performed in nowadays than anything else.

Maybe he just walked on stage with a Casio at the appropriate moment.

As for the discrepancies, my feeling is that in terms of things like phrasing they would have been part of the music so to speak, comparably to (but obviously not the same as) what happens in jazz groups. I would imagine not only that Allegro wouldn't always be the same speed but that any given Allegro movement wouldn't always be performed at the same speed by the same musicians. I suppose when I said "conductor" I meant more a kind of "MD" like Reinhard Goebel rather than a "proper" conductor like JEG.

I have often wondered that myself. I suppose it must be that singers are much less used to being led by an instrumentalist than other instrumentalists are.

Thinking about it more, I suppose it shows up an unfortunate divide in how instrumentalists and singers are taught.  I'm sure in the 17th/18th centuries, everyone was expected to sing and play (more than one instrument of course), would have understood each other better and would have been able to lead/follow each other more easily.  Most singers I know maybe have a bit of piano but gave up any other instrument long before reaching the stage of understanding ensemble playing well (and the piano is not conducive to that, especially as a second-study instrument).  I know a few instrumentalists who have sung a lot and it's interesting to get an insight into how they understand what singers are doing.  But for the most part everyone is pretty ignorant of what the other group does.

As for string section size - certainly among the British groups financial restraints (if nothing else) have led the way towards smaller sections (opera productions being an exception).  AAM is hardly ever larger than 4,4,2,2,1 these days.  We're doing a Haydn programme next year with six fiddles total.  It may be for gloomy money-related reasons, but it's led to some very interesting playing (I think).

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Just saw Robert Dahm's post.  Yes of course a choir needs to be together within itself, but so does an orchestra.  Why is there such a divide between the two, while there's no such divide (well, usually) between diverse elements within a self-directed orchestra (string/wind for example)?  It's not just a matter of choir-adapting-to-orchestra - the ideal is to create a whole ensemble that can be kept together through chamber-music-like techniques, or a MD playing an instrument (for practical reasons - the lead violin/cello or keyboard is the only person everyone has a chance of seeing without turning their backs on the audience).

But I'm mostly thinking of choirs of no more than 3 per part, where the responsibility is similar to, say, a small string section (where in larger groups it is equally wrong for individuals to stand out).  They may be able to direct themselves, but put them together with a chamber orchestra or HIP ensemble and suddenly there's a great necessity for a carver, any carver.

Maybe it's also a sign that we don't really get enough rehearsal time (again down to financial considerations).  If we all had a chance to get used to such a set-up, it probably would eventually work well.  But with typically 3-9 hours rehearsal if that...

I wish I had your problem. In my experience, many choruses, even ones with a highly cultivated and professional sound, have trouble coping with an armwaver other than their usual director.