In a sense, it is. Since both are at their best as ball-dominant scorers/play-makers, playing either off the ball wastes their talent. While they trade off doing it a bit (which doesn't change that talent is being wasted), McCollum is generally the one off the ball. Turning McCollum into a JJ Redick a lot of the time is inefficient, since McCollum could do more. Trading him to a team where he could be a slightly-worse Lillard and getting back someone who's talents are maximized alongside Lillard would be a more efficient use of talent. That's why doubling down on strengths isn't ideal (and doubling down on their weaknesses is crippling).
Yeah, playing the 47% 3pt shooter off the ball as a spot up option is totally wasting his skillset...
You're acting like McCollum always needs to ball to be effective, but that couldn't be further from the truth. The dude is one of the top 5 3pt shooters in the league, and is just as efficient as Redick. Yeah, he can do more, so have him attack closeouts that are too strong to get an open shot off, and let him handle the ball to take the pressure off Lillard. That's what they do. How does that mean their wasting CJ's talent.
McCollum is just as good spotting up on the wing as he is with the ball in his hands. You're turning that into a negative by saying CJ shouldn't be used as a spot up shooter in some scenarios because "he can do more". That's like saying you shouldn't let DeMarcus Cousins post up because he can do more than post up...
CJ's spacing helps Lillard, and vice versa. Their skillsets help one another, not hurt them. CJ is such a great shooter and ball handler that defenders don't play off him often because he'll hit the three or attack the closeout very well.
You're logic makes sense in a Nate McMillan offense, where there is one guy iso-ing and trying to get buckets while everyone stands and watches. However, their ability to play off each other and score from anywhere on the floor benefits each other in any type of offense where the players move the ball or play off of each other.
The "Doubling down on strengths makes those players less effective" theory is one of the dumbest theories I've ever heard in regards to Lillard and McCollum. It makes sense in very specific scenarios but people try to apply it where it has no merit.
It would make sense if you had a starting lineup with Rajon Rondo, Giannis Antetokounmpo, and Ben Simmons. They all pass well, but none of them can shoot. Therefore, all their passing gets collectively wasted because none of them are scorers.
But how does that work with two guys that are so dynamic offensively that they can play on and off the ball, both handle the ball, both create for others, both hit mid-range and 3pt jumpers off the dribble, both play in the pick n roll, both spot up and hit shots and attack closeouts, and both move well without the ball and are comfortable coming off pin-downs, flare screens, and make the right backdoor cuts when they're overplayed?
Sure, with Crabbe and not McCollum, Lillard would have to shoot more. He'd score over 30ppg, but on a less efficient clip due to the lack of a threat at the SG position, THUS making Lillard less effective himself without McCollum (and vise versa).
There is no way that playing Lillard and McCollum together isn't maximizing what both of them can do. I understand that neither are good defensively and how that's a problem when neither of your guards can lock down one of the oppositions guards, but their offensive skillsets are so versatile offensively that they would compliment any guard in the league very well because they can do anything and everything offensively.