Well, Mahler only lived to the age of 51, and composed his nine-and-a-half symphonies and his song cycles from Des Knaben Wunderhorn onwards over a period of less than 25 years (a composer who received commissions for all of those works during that period wouldn't be doing too badly today). During this time, he was also heavily occupied as a conductor with major orchestras and opera houses, which I imagine provided the bulk of his income; if he wasn't doing all of that, maybe he would have composed even more, not necessarily of any lesser quality? He was by all accounts an extremely talented conductor - not all composers have comparable skills either as conductor or instrumentalist, but still need to be able to make a living. I find the commissioning circuit deeply problematic, but I'm not sure if I know of a better alternative.

No, we don't. Mahler's symphonies for various reasons took longer to write than Haydn's. This isn't in any way a reflection on their quality. Nowadays the (financial) pressure is for the Mahlers among us to write their symphonies as quickly as the Haydns, and I think it's clear that this could lead those Mahlers to churn out more stuff than would be consistent with the kind of evolution and the kind of quality that the real Mahler had. And if anyone doesn't like Mahler as an example, how about Varèse, who didn't write very much at all, partly because he was attempting to rethink musical composition in (what I believe is) a much more fundamental way than Schoenberg, in such a way that the results of this rethinking are rather few and far between. Or indeed Webern. (Come on, Anton, you lazy sod, those pieces of yours are so short you ought to be able to write half a dozen of them a week!)

Don't forget though that Webern actually DID complete a fairly substantial piece of work as a doctoral student: his study of Heinrich Isaac's Choralis Constantinus which he produced while studying musicology in Vienna.

It was all coasting from there on, obviously.

I thought is was me advocating it! Anyway, if Ian also is, all well and good.
That's right. And it certainly is unavoidable, but going into a project with a "take the money and run" attitude is certainly not going to help.

I think the implication of the colleague in question was that once one's "career" has achieved a certain level and momentum one can easily get away with producing a pup now and again.

Well, I can't think of a single contemporary composer who comes anywhere near matching Haydn's level of productivity.

Actually, I do favour the stipendiary system overall, but don't see it as so fundamentally different to the commissioning circuit. For a start, decisions have to be made as to who well be given a stipend - as with commissions, that surely has something to do with their previous track record (though of course all sorts of other political factors inevitably come into things - also this sort of system can put a tremendous amount of power into a small number of hands, which might not use that scrupulously; the same is true of commissions, though the stakes are slightly less high). And then, are they just given such stipends for life, or should they be subject to conditional renewal? If not the latter, what's to stop someone getting a stipend and producing practically nothing? Presumably some sort of bottom line needs to be created in terms of productivity if stipends are to be renewed, say, every 10 years or so? And isn't it likely to cause some ill-feeling if one composer receives the same stipend as another but whose productivity is 5-10 times greater, perhaps because the other composer is making more money on the side doing other things (such as conducting)? How to deal with these problems? If there is some bottom line in terms of productivity, isn't it just like saying 'here's a commission for a minimum number of pieces', though allowing some more flexibility in terms of forces, nature of the work, etc. (but then there are still issues of performances). And as such that's all someone can make, unless they supplement their income with, er, commissions (maybe from abroad)?

Some of the issues very much mirror those of tenure in universities.