Easier? Phoenix did very well but it was a really hammy peformance which the movie completely served on a platter for him to over indulge. Ledger had to work within the confines of being one of the characters in a film rather than canvass especially put up for him to do his acting thang. And Phoenix in the time that he was the Joker showed that it isn't really to be that enigmatic iconic character. He didn't have the voice and intimidation when did portray the Joker. Each did well in their domain. I don't believe one is much easier than the other.
Psychopaths aren't necessarily more enthralling. Walter White remains the most fascinating character I've seen in any piece of entertaining - film, shows etc and he wouldn't fit that description. He was nuanced and he was human rather than being overly manic. But it was as incredible a peformance as I've seen. It helps when your script is miles better than the Jokers of course but it is what it is. For me, Joker was a good film but predictable and unoriginal (clearly) which makes the lead protagonist as well to an extent those things.
You're skipping context here - I said: 'it's far, far easier to play a psychopath than a possible paranoid schizophrenic descending into a state of mental collapse.'
You've mentioned intimidation more than once whilst not considering, that fundamentally, one version of The Joker (psychopath) conveys that, whilst others (in this instance, the one trying to keep it together as a normal, functioning human being) simply do not. As I said, a follow up movie, which delves into a sociopathic Joker and thoroughly explores him as a fully invested deviant would determine what Phoenix could do with the character in a direct comparison - his Joker, in this film, was supposed to display, vulnerability, angst, weakness and a whole host of other things that have
nothing whatsoever to do with psychopathic Joker of
The Dark Knight.
Your second paragraph: Walter White is not a psychopath. It is very important that you make the distinction as otherwise, there are no layers to delve into - sociopathy can be triggered or descended into, and Walter White displays that in exemplary fashion. In the first seasons, it is very clear he is a normal person, with genuine feelings and emotions that aren't dialled down or accessibly switched on or off. His trauma triggers him and turns him into the beast he ends up being, very much like Phoenix's Joker. There is literally none of that, zero resource, shown in Ledger's Joker because it is not the same thing. It's easier for me to put this up than go on and on:
All throughout the film, he exemplifies psychopathy - to that end, the depth is pushed outward for the viewer to see with very little implied and no journey for you to go on with the character as he transforms from one being to another, as you will see in any sociopathic potrayal with an origin story attached. Cue your: Tony Soprano's, Walter White's, Phoenix's Joker's and so forth as opposed to your Anton Chigurh's, Gordan Gecko's, Ledger's Joker and so on. One is much easier to make a film (singular) out of and the other is better suited to TV, or at least, a series of films that let you see the beginning, middle and the end as you (we) get to voyueristically observe.
As I say, seeing Phoenix, fully-fledged, if you will, off his meds and fully transitioned into an uncaring and detached individual would give a fair comparison on what Phoenix can or cannot exude as a fearsome Joker. In this film, the tidbits we got at the end as he started to dip his toes in that proverbial water is about right. The way the role was played lends itself to the questions that should be asked as to why this character wasn't helped along the way with an intervention staged and that is what it was supposed to do. Low key with a few spikes, as opposed to fully turned up dial of the type of Joker you prefer (one with menace, charisma and all that).