I understand what you are saying Cno, the subjective differences between the amplifiers listed would be agreed by many on here and elsewhere.
However, such evidence as exists would strongly suggest that this is not the case. Ignoring nonsense such as amps with 10dB bass boost, then compedent amplifiers such as those listed will all sound very similar indeed when tested rigorously.
Providing the amplifiers are working within their specified output, carefully matched for level and auditioned blind, then I reckon that few on here would be able to pick the differences. I know that is a big assertion and possibly some listeners would be able to pick amps they know very well, but it coincides with my own experiences and the results of other blind tests.
Most of the differences heard in sighted tests are generally accepted to be the product of expectation bias, but I do wonder if there are other factors at work too. Some amplifiers seem to be able to make you play them that touch louder than others, often something as simple as sensitive volume control can make the difference.
Arcam amplifiers have a reputation for sounding smooth and a little 'laid back', and, surprise, surprise, they have sensible 'slow' acting volume controls and are not unduly sensitive, input wise. Compare that to, say, a classic 'exciting' Naim with fast acting volume and highly sensitive inputs.
Without measurements it is impossible to compensate for these differences, and this is just one area where the design of these amplifiers affects the way they are used and therefor percieved.