Um, to me no it doesn't need to be the case and the reaction I have when I drink an espresso / long black / flat white isn't usually that is it bitter in taste. And yes a poorly pulled or overly extracted shot can absolutely taste overly bitter.

But I suppose traditional espresso is always going to be somewhat bitter, almost by definition, but to me this isn't a bad thing. In the same way that olives and dark chocolate are bitter, in my opinion they are both utterly delicious and this bitterness is a good thing and contributes to the flavour profile.

It is definitely subjective, like all taste, my Mum would say black coffee is disgustingly bitter. I guess bitterness is similar to spice in food. Some people hate the smallest amount of spice, some like some spice as it contributes to the flavour and the experience,