45% from the field for a perimeter player who shoots a lot of jumpers is not outstanding, but it certainly isn't pathetic. Especially in this era of basketball where defenses are better than in the 80s and 90s. Look at a sharp shooter like Ray Allen, and his career FG% is right at 45% too. Ginobili, Paul Pierce, Vince Carter, T-Mac, Joe Johnson all the same or under 45% on their careers.
LeBron and Wade have better FG% because early on in their careers, they attack the basket much more. The ability to do so and more so the ability to finish at the rim when they do attack is what makes them very special players. Then there are the rare few perimeter players that are just able to shoot high percentages, like Nash, Chris Paul, Tony Parker, and Wally Szczerbiak for whatever reason, generally because of their shot selection, similar to John Stockton. They almost always take good shots, open shots, and generally don't force tough jumpers that are well contested.
Kobe attacks the rim, but less frequently than guys like LeBron and Wade. He just shoots more jumpers than he does lay-ups and dunks on drives. 45% FG is more than adequate for a superstar wing player in today's NBA. Could be better, should be better. But it's not pathetic. It's also important to note that if you take the three years after Shaq was traded out of the equation where Kobe was often double and triple teamed and also forced a lot of shots at the end of shot clocks, he would be closer to about 46.5% FG shooter, which would be very good for a perimeter player in today's league.