Stem arranger: Yes, you can record, edit, play, sequence and mangle samples and also create full songs, but it’s not a DAW. The Octatrack isn’t either though. They’re both more like groove boxes with sampling features.
Clean filtering: Depends. Some of the analog filters can be clean and one or two of the digital filters as well. But it’s not meant to be a clean filter effect box.
Sampling quailty: Yes, sampling quality is great, as far as I can tell.
Time stretching: It’s an effect to deform audio mostly, so not really clean at all 
Sequencer: It can do swing, even per step, and is very very capable. No parameter locks like on the Elektron gear, but instead you get sequencer morphing.