Jamal after about 08-09 went from just jacking up shots to actually doing it efficiently, that is when his career changed and he became a more valuable player.
Jamal despite the general thought has never been a great scorer in his career. This seasons 21.9 pts/36 is his career high scoring rate. He didn't reach a scoring rate of 20 pts/36 until I believe his first season in Atlanta. He's generally been a guy hovering around 17-19 pts/36 most of his career, but that year in ATL and then the last two seasons in LAC have been his only three seasons with scoring rates of 20 pts/36 or higher.
His ability to explode and get hot as a scorer has been confused with being a great scorer, but great scorers are more consistent than what Jamal had shown through his career, which is actually what made coaches think the bench role was better. He was/is a ball dominant guy (though he can catch and shoot very well) who didn't give enough consistency as a scorer each night or playmaker and didn't defend well enough nightly to easily justify starting him.
The consistency we are talking about doesn't mean every single night, but a general consistency, which is why their averages end up being high because most nights they are in the range. So while great scores have their hot games and cold games, night in and night out, they generally give a good rate of scoring. CP is not as explosive in terms of a one game blowing up scorer as Jamal, but he's easily been a better scorer for their careers for example, but most people wouldn't think that based on perception, but night in and night out in their careers Chris is a guy who has produced superior scoring production.
I think Jamal plays a very nice role for his team. I wouldn't say he is irreplaceable in the way CapsNClips is saying because we have Manu Ginobili, Nate Robinson, J.R. Smith, and before he declined to suckitude, Ben Gordon was also a player capable of doing the same thing and willing to come off the bench who would fit based on the team need / dynamics. Now I know not all those guys (eg: Smith) are playing well now, and Robinson is injured, but Smith has fit that role well in the past and Robinson was good for the Bulls.
Also we'd have to give mention to guys like Rodney Stuckey on Detroit, Dion Waiters on Cleveland, Tyreke Evans on the Pelicans who are all playing similar roles in terms of scorers / ball handlers / playmakers off the bench, though I'm not claiming equal effectiveness from all.
I can't gauge all of their willingness to come off the bench either, though we at least know guys like Manu, Smith, Gordon and Robinson are content there, and at least in the right situation I'd imagine at least 2 of those 3 other guys are also.
I'm just mentioning guards, I supposed Blatche and Amare are also 6th man like scoring big men though the guards seem to get more of the props for that role.
I would easily argue that a guy like Ginobili not only replaces, but supercedes Jamal as a superior playmaker and defender while being a similar level scorer and shooter, and capable of properly playing the SF spot and not being undersized. Of course his recent finals blunder still is remembered by the masses, but that doesn't make him any less good. Now of course I don't think we were talking about any realistic ability of getting these said players that could replace his role, just whether there are such players, and there are.