He's the opposite of Rajon Rondo.
Let me explain.
Toine was a wildly talented player with a vast skillset and reportedly a great Bball IQ. He joins a terrible organization. A front office who didn't know what they were doing. A culture defined by losing. A coach who was in over his head. No veteran mentors to set him straight. Within a couple years, he was basically given free reign to do whatever he wanted... He ruled this organization and was given superstar status when it wasn't warranted. He didn't play the game the right way. Whereas he always had talent around the basket, he decided he wanted to jack up threes almost exclusively. The team didn't share the ball... even when they were a 44 win playoff also-ran, it was a 2-man offense with Walker getting to do whatever he wanted. When O'Brien took over he basically told Pierce and Walker they could do whatever they felt like on the Offensive end as long as they committed to the defense. What you ended up with was a spoiled talent. At his peak he had shooting percentages of 38%/32%/61%. That's obscenely bad. He's the pure definition of "volume scorer". He also didn't handle himself professionally... the wiggle was classless. He would have never done that had he come up under veteran leadership. He was never deserving of the "franchise" label he received here and most of us who followed the team closely during that era recognized it. Danny Ainge was smart enough to see this and one of his first acts was to ship Walker out of town.
I loved Walker, but he was a spoiled talent. He came into a bad situation and it ruined what could have been a much better career. It's the kind of stuff they refer to when they say that DeMarcus Cousins needs a new scene. Cousins could be an all-time talent with the right mentorship, but he might never reach it on the dreadfully run Kings.
On the flip side... Rajon Rondo.
Rondo was an "ok" prospect. Mediocre College career. Mediocre skill set with serious flaws. Not a lotto pick... not even a top 20 pick. But he was someone who had potential. Rajon's first season wasn't great. He started it 3rd in the depth chart and worked his way up to back-up. But he joined a smart and well-run organization with a respected coach. His second season, he was thrown into a situation where he was a default starter on a team whose identity was defined by (at the time) a Top 5 player in the league. There was just no way you would slack off under KG's watch. Additionally, he had an all-star OCD perfectionist/"pro's Pro" as his direct mentor (Ray Allen). And of course there was a 3rd veteran star on the team who lead by example (Paul Pierce). In addition to those guys, you had quality veterans like PJ Brown and James Posey on the team... and later in the season they added a veteran all-star PG to come off the bench (Sam Cassell). His coach was a former all-star PG. His GM was a former all-star PG. It was absolutely the best-case scenario. Every step of the way, Rondo had mentors, the best possible situation, a winning culture, great leadership in all areas of the organization, a system in place that would allow him to grow step-by-step and eventually catered to his strengths and weaknesses. His third year, they brought in a headcase all-star PG to back him up... Rondo surely learned a few lessons in practice from sparring with Stephen Marbury as the player flamed out. "Here's what NOT to do, Rajon". Rajon evolved into one of the elite PG's in the league. An all-star player.
It's like Gladwell's Outliers. Your success is as much dependent on your surroundings as it is the work you put into it. Had Rondo joined the dreadful organization that Walker joined, I don't think he ever reaches all-star status. Had Walker joined the team Rondo grew up on, it's possible he would have evolved into an all-timer. I legitimately believe that. Antoine Skywalker joined a soulless franchise and went to the dark side of the force. Rondo Skywalker had mentors like Obi-Wan and Yoda (KG and Ray) guiding his way and making sure that he became a proper Jedi Knight.
If this was a video game, Walker probably joined the league as a 71 overall with 90 potential... eventually ending up as a 76. Rondo probably joined the league as a 61 overall with 75 potential, but somehow vastly exceeded all expectations and ended up an 81.