Cant really use that argument, AJ has fought his fair share of poor boxers plus lost to one of them.
Ruiz was 12 in the world, he has his limitations but he can absolutely punch and had never been down. He's way above all but 2 of Fury's opponents. Which top 20 ranked boxers (at the time) has Fury fought? Remember also that Ruiz was a stand in, as he was due to fight Miller who was even higher ranked. Look at the last 10 fights for these guys:
AJ:
- Dillian - 16 unbeaten, a tough nut, aggressive. Wasn't top 10 at time but was clearly going to be
- Charles Martin - IBF champion, unbeaten and KOd last 10 opponents, top 10 boxer at time
- Brezeale - an unbeaten champ top 10 at time
- Molina, top 20 boxer, had only lost to Wilder and Arreola
- Klitschko - legend
- Takam, was a stand in and top 15, His only defeat was Parker and he had never been on the floor
- Parker, unbeaten champ and top 10 boxer
- Povetkin, granite, long term top 10 boxer, had only lost once to Klitschko, had never been on the floor
- Ruiz - 12th in the world, a stand in, had only lost once to Parker, never been on the floor fought twice
Fury:
- Joey Abel top 50 boxer, had 7 defeats already, had been KOd 4 times
- Chisora - wasn't top 10 at this time, and had lost 4 of his last 10 fights coming into this, still was a top 20 opponent
- Christian Hammer - top 30 opponent, but had no real resume to speak of
- Klitschko - legend
- Seferi - top 50 opponent - had no resume at all
- Pianeta - top 40 - had at least been in with some decent boxers, but come off second worst to them
- Wilder - rubbish boxer but great puncher
- Schwarz - top 40 - hadn't fought anyone other than germans and czechs
- Wallin - top 50 boxer - no record at all, but managed to gauge Fury's eyebrow to pieces
- Wilder - rubbish boxer but great puncher
AJ hasn't gone outside the top 20, AJ has fought 6 of his last 10 against tomato cans.