Process vs Outcome orientation:
Turns out people are different. Who knew?
Some people really value the process or "journey" that is required to reach a goal. Some people value the process so much that the end result's value, in their eyes, can change depending on what the process used was. An extreme example of this is seen in the common saying, "It doesn't matter if you win or lose. Its how you play the game".
Other people care less about the process and focus more heavily on the goal or outcome; way the reach the goal matters less or sometimes doesn't matter at all. "Win at ANY cost" is the extreme end of this thought.
Neither way of thinking is INHERENTLY better or worse, good or bad. It is a subjective thing.
People who value outcomes more than they do the process are more likely to cheat. I admit that that is a major oversimplification of the situation but I don't want to type too much more so don't flip out please.
Player A is willing to be boosted because the vast majority of the value, to HIM, is obtaining the objective award. Getting the border, ward skin, etc. He isn't bothered by the fact that he really isn't "that good" because he doesn't value the actual skill. It's all about the outcome.
Is it wrong for him to value the border more than the skill? No.
Is it wrong for him to get boosted in order to get the border? It is certainly against Riot's ToS.
I'm not claiming that this is the absolute truth in every scenerio. I'm just applying the "process vs outcome" concept from psychology to the OPs context.