Great post. I was going to post something similar. The answer your question, the amp should do what the owner wants it to do, or people should buy the amp that sounds good to them.
That being said, my goal is to build a system that is neutral from the streamer, to dac, to amp. Why, because I want to have less variables to contend with when I buy my speakers. If I have 3 or 4 variable, trying to then pair it with a speaker is tricky for me. If I have a warm amp, do I need a bright speaker if so, how bright? If I get a warm speaker is the sound going to be too warm with my warm amp. Throw in a dac, and it more complicated. It is like to solve a 4 variable differential equation.
The second reason is that for this system, I want to hear what the band/singer and producer/mixer decided on and felt was their product. Maybe it sounds great, maybe the recording is too bright for me, but I want to hear it as they intended (as best I can). I don't want to have my system impose coloration on the sound and I accept the consequences. I know it won't be perfect, but I want to give it ago and I can use the speakers that I demo to adjust the sound if needed. I can demo speakers at my house, or even take my amp and dac (both small and light) to the store. Much of the fun is in the process and the shopping.
I also support everyone to customize their system to their preference. If you like warm syrup, that is great. If you like bright details, that is great too.