For many species it is possible to provide appropriate social groupings, hotspots in enclosures, substantial indoors and other sheltered accommodation and so on. Not so for many "hoofstock" species. Is a couple of zebras shivering in a muddy paddock really a good exhibit?
Welfare and conservation are indeed paramount - however, when the discussion specifically pertains to the strengths of a zoological collection in a certain field or category, arguing that a collection which has little-to-nothing to offer in the category should win with a clean slate *because* it has little to nothing to offer and therefore has no shortcomings is
significantly more unfair that the randomised selection of categories and zoos which you bemoaned upthread

It's a bit like saying that Highland Wildlife Park is a better zoo for tropical species than Singapore, because HWP would be a terrible place for species adapted to hot climates, but they stick to their strengths and collection focus, and therefore do not keep such species!
As for your suggestion that
"it seems to me this competition is about adding up the number of species, then modifying the result if there are a few nice enclosures" you obviously didn't see how hotly some of the worldwide cup matches last year were debated, and how near to the wire some of them came! For instance, several individuals (myself included) made a pretty fierce case for Chester being a better zoo in the "Island Species" category than Taronga, on the basis that the former is actively involved in a large range of conservation projects relevant to the category and moreover has a pretty damn good collection of relevant species
without having the in-built home turf advantage that the latter collection has being based in Australia.
We lost, but by rather less than you might initially imagine.
The ironic thing is, I'm not even all that keen on Colchester myself

but even so I can say pretty firmly that your automatic assumption that all they can offer is
"a couple of zebras shivering in a muddy paddock" in summer and animals
"no doubt confined to some dark and cramped stall out of sight" in winter is entirely inaccurate.