The 50/2.8 macro doesn't do 1.0x maginification either. That's probably why it can perform OK at non macro tasks.
I don't see the evidence for this. You've caught me out in the sense this was not a good example I mentioned of a macro lens doing well at infinity because the Canon 50/2.8 only does up to 0.5x life size as you say. However, there are a number of other brands of 35mm macro lenses that do
1:1 life size and that have even better Photodo ratings than the Canon 50/2.8, such as the Minolta 50/2.8 and 100/2.8, both with a rating of 4.5, and the Pentax SMC-F 50/2.8 with a rating of 4.6. Even the el cheapo Tamron AF SP 90/2.8 does 1:1 macro and has a photodo rating of 4.3.
Consider the MP-E 65mm... doesn't focus out to infinity at all AFAIK, and couldn't be tested at all with Photodo's methodology, but it is quite useful for the right kind of macro photography.
That's a true, dedicated macro lens that enlarges to 5x life size without extension tubes. It's not designed to focus at infinity as all true macro lenses are not. One could argue that the term 'macro' lens for lenses that behave normally is a misnomer. Perhaps they should be described as 'close focus' lenses.
It's all about tradeoffs IMO. If you aren't interested in macro there is probably little point in buying a macro lens
I think you'll find there are a lot of folks who have bought the Tamron 90/2.8 macro because it's a sharp, good value lens, with or without macro. For many, the macro facility is just a bonus. But you have raised a point that hasn't been resolved in this thread yet.
I've made an assumption that the superb plots for the EF 180/3.5 macro in Canon's Lens Work books are an indication that at some close focussing distance this lens really is superb. But this is no more than a reasonable assumption. I have no evidence that it might be true, other than Canon's own theoretical MTF charts, the fact that the lens is a fairly expensive prime and a few subjective comments to the effect that it is a sharp lens.
As much as I am loathe to criticise anyone who is friendly enough to post an image demonstrating the quality of a lens, I have to be blunt and say that it's impossible for me
to assess the quality of the lens that was used for the shots in this thread. For all I know, this lens could have a 3.9 rating all the way from infinity to its minimum focussing distance of 480mm. On the other hand, it might be even worse than 3.9 at closest focussing distance.
Without proper tests and comparisons I'm afraid it's all airy fairy and subjective.