The only reason he's not picked at RW for every single Manchester United all time XI is because Ronaldo is a freak of nature who is arguably the greatest player of all time.
Beckham had an immense passing rate, incredible accuracy, superb vision, perfect deadball ability, was the best crosser ever (arguably), excellent work rate and good footballing intelligence.
His only weaknesses:
1. His left foot was for standing on only. Consider how immense his right foot was though.
2. He wasn't very quick. He wasn't slow, but he wasn't the fastest player on the pitch. He could beat a man, but he wasn't going to dribble past 4 or 5. He didn't need to. He could pass from anywhere to anyone.
3. His celebrity was so high, it overshadowed his footballing abilities, but never his performances. There isn't anyone like it today. Ronaldo, Neymar maybe? Idk what thier hype is like in Brazil and Portugal but Beckham was a sporting icon.