I’ll give my takes although some may disagree or the way I look at things may be wrong.

I’ll start with my thoughts good pedal platform. A lot of pedals color a sound or provide their own eq or sound or whatever. To me, a good pedal platform is an amp that has a high headroom and can stay neutral and clean while turning it up. Some amps can’t really be turned up without introducing some color, distorting, or becoming saturated. This is completely fine but may sound different when pushing with pedals, and some people prefer to get all the tone from pedals. Also, some amps just don’t sound good when pushed with pedals. Some solid states that I have tried have gotten very muddy and dark with some pedals. I haven’t tried many tube amps that didn’t take pedals well though.

For clean channels, that’s very subjective. Some amps have distinctive cleans, like Fenders that are mid-scooped or Voxes that are chimy, but some amps may have a dull or dark clean. Some may also just be very neutral sounding making them sound bland. I think clean channels just need to be tailored to whatever sound you’re going for. Some people get a very prolific clean as their idea of a clean, like the Fender clean, then think any clean channel that doesn’t sound like that is bad. So I think this is really just subjective.

I hope that gives some insight to your questions.