He was number 1 at 140 and i'll explain why. Back in 2010. Khan, Alexander, Bradley and Maidana were considered the best 140 pounders and all faced each other (Khan facing and beating Maidana and Bradley facing and beating Alexander). This left Amir Khan and Tim Bradley to fight and decide who's the man at 140, but of course Bradley was offered the Pacquaio fight and chose not to fight Amir at the risk of losing and jeopardising the bigger fight (which is fair enough). After this, Khan unified the division and became super champ with the WBA/IBF titles and was therefore left as number one of the division by default.
Khan was unfied champion at 140 , and No.1 in most ranking when he held the Super WBA and IBF titles Khan at current ranked No.1 at 147 being a mandatory to the Champion Garcia by the WBC..
That being said, his No.1 stat at 147 is just a technicality. He was only ever truly number 1 of a division at 140 where he pretty much fought everyone available minus Bradley.
You are one of the few people who see it ever so clearly. People let their bias for others lift one guy over the but when you take a look at Khan's entire career it was filled with Good Ole British stoppages were the opponent was still standing and ready. He was protected until Prescott upset him.
We Need Bradley Khan ONLY ARUM can stop this fight now! I bet it would be fight of the year. Both landing their own variation of punches. High work rate. Both tiring at times. Both have surges! It would be amazing! Both hurt each other at times but not enough for a stoppage 12 rounds of great boxing. The only thing which would ruin it is if Bradley goes full bumrush and it turns into a clinch fest.
After Pac left the division. Bradley clearly becam number 1 when he beat Devon. That was January 11. In November 11 he then dominated Casmayor before leaving for the WW division. During this time everyone expected Khan to take a hold of the division, however he then lost to Lamont. And even if people don't see that as a legit loss, which is fair enough given the failed test, but Khan then lost to Garcia in a legit stoppage. So there was a period when he was the favourite to take top spot but it didn't happen. Over confidence cost him in back to back fights. Since his move to WW he's failed to beat the top man, but given the departure of Floyd and Pac, it could happen for him. Garcia, Brook and Bradley are all winnable fights for Khan.