"I see alot of websites and blogs that claim that the key to becoming a successful jazz musician is to load up on licks. Now while this may be useful to create mood in some contexts, it's not possible that licks alone can make a jazz musician. If this were so, jazz would be easy, and everyone would be great, given that they were on the same page for technical proficiency."
I disagree with your premise wholeheartedly. A lick based approach to any kind of music does NOT make it easy. How can you back this up with data.
If you want the question to provoke serious thoughtful response can you define a "lick". One could say that a 4 octave run fit into one beat is a "lick". One could also say that the first 16 bars of Paganini's 5th caprice is a "lick".
Knowing a lick, or a library of licks doesn't translate to using them intelligently every time. It still takes skill and effort to make a solo out of them. Also, using standard licks does not mean you are not improvising. I am improvising this answer using words and phrases common in the English language. I will not make up new vocabulary as I go, nor will I redefine grammar or introduce uncommon slang. I will not attempt to express this as William Burroughs might in Naked Lunch. Yet this will be uniquely mine. As some other answers have pointed out music is a language and the deepest understanding and use of that language is improvisation (IMO).
There are many schools of thought on what it takes to improvise and even what it really means. Make no mistake, improv involves using what you know in a unique way in the moment. But you have to know something! In it's simplest form variation on a theme is improv and for many that is all you need. People get into heated arguments about originality on this point but if you really analyze a player's work you will see patterns emerge, no matter how unique you think they are, they are drawing from rehearsed lines to some extent. If you transcribe enough music you will see common melodic themes, memes in the Dawkins sense of the term, replicate and propagate through the generations. The originality in many cases is in the phrasing and other subtle nuances and not in the note stream itself. In a very real way improv is more about how you say it rather than what you say. 1000 players can say the same thing but perhaps one or two stand out as sounding original.
I cannot speak to Bill Evans. I have several CDs of his work and love it but have not committed to transcribing it. I have arranged Oscar Peterson piano "licks" for guitar. I wouldn't say he's entirely "licky" and all bluesy. But he is famous for the opinion that a blues phrase is essential for playing jazz. I will say that I have embarked on the journey of transcribing solos of players I though were more "original" than others only to discover when I was deep into it that some of the classic 50 year old memes were being used prolifically.
"In contrast, Bill Evans seems like the pianist who barely uses "standard" licks. And if he uses licks, he has so many that he only rarely uses one more than a couple of times. In my opinion Bill Evans' playing is melodically "fresh" i.e he really puts new ideas on the keys every time he plays."
There seems to be a little bit of a contradiction here (correct me if I'm wrong). If you think that Bill Evans "has so many (licks) that he only rarely uses one more than a couple of times" doesn't that support the idea that the key to great jazz is learning as many licks as possible? As I said people get into heated debates about this but in the end it's and art form so trying to reduce it to a formula will always fail and people will gravitate to approaches that make sense to them, perhaps for personal and subjective reasons. But every form of music I have heard in my life uses "repetition" of melodic ideas and rhythms to create a pattern. People like patterns. So if you don't apply some repetition to the work it will likely be perceived as non-musical. Whether that repeated piece is a blues idea or not is material.
One of the best jazz improv lessons I have learned in my life came from reading Jerry Coker (and having this reinforced by my teachers) that one should keep a diary of melodic ideas, as short as 3 notes and as long as a whole section of a tune. These don't need to be lifted from other but ones you have written your self. Then over time you are using a lick based approach but the licks are yours. Perhaps Bill Evans had done this early in his career.
Based on the meaning of the term "Lick" as it was taught to me, Licks alone make up everything.