That's what I believe. Sure, the best attacking players have an innate sense of how to beat a man, awareness of space on the field, or ability to play a killer pass. But, in my opinion, defending is such an innate skill - the timing and senses required, as well as knowing where to be on the pitch to cover space before a pass is even played - that I'd rather take a rock solid defensive player and set him to work on his body feints and crossing technique than take a natural born attacker and expect he'll learn how to defend well.
Take Valencia for example - great old fashioned winger in his day, who had average success as a converted fullback due to his physical ability, but was often found out for lack of positional awareness and generally horrible sense for when to tackle and when to back off his man.
Even if AWB will never be as naturally gifted going forward as someone like TAA, it is objectively true that he could improve his crossing ability solely by spending countless hours on the training ground working on his technique - crossing is a skill like free kicks, in that way.
Maybe this is just personal bias from my own experience - played winger for the first 18 years of my life, converted to wing back for the last 5-6 years of my competitive playing career, now play casual co-ed leagues because my knees are gone - but high level defending is a much harder skill to teach than certain attacking skills that would round out his game nicely.