Kell wasn't with Matchroom (Eddie Hearn) back then, he didn't sign with Eddie until 2011. Brook was notorious for not taking boxing serious, always missing weight, always in nightclubs and what not getting into trouble. He was beat up and stabbed in a nightclub long before his famous stabbing after the Porter fight. He fell out with several manager/promoters and even got kicked out of his current gym, Ingles, where he started boxing, before reconciling with them.

That's why during that period, not only was his competition just British journeymen, he was so inactive for a prospect. Even when he left Frank Warren for Eddie Hearn they predicted he would never amount to anything because he was too unprofessional.

He didn't have extensive amateur experience, he only had around 30-40 bouts, and didn't compete in any major championships, although was touted as a talent to watch.

The losses of his opposition means nothing. Errol Spence's trainer keeps bringing it up and i've seen it mention loads of times since by Spence fans/American pundits. However, during that period he faced some of Britains well known "loser" journeymen several times - Peter Buckley (189 losses) Earnie Smith (263 losses) Brian Coleman (139 losses). They have roughly 600 losses between them, so basically three opponents completely distort the figures.