In my opinion “bitterness” is a very broad subject and really subjective. I find bitterness in whisky a lot of the time can be associated with youthfulness - sometimes very unpleasant, however sometimes the bitterness can be cut by adding sherry casks into the mix, which can “mask” some of that youthfulness, resulting in an interesting, complex dram. I like a little bit of bitterness in whisky, but the balance needs to be right - returning sweetness, so you get that mix of bitter/sweet.
Similarly, I used to drink a lot of puerh tea daily - my favourite puerhs were always those that had some bitterness in the background, however again like whisky, balanced with some returning sweetness.
Today I have had x2 shots of espresso - both had some bitterness, however I would liken it to 90% dark chocolate rather than just being “bitter”. There were other flavours which did help to balance it all out. So, basically I really don’t mind some bitterness in my espresso, as long as it is balanced out by all the other flavours.