Hon lost 10 out of 10 fights against Zahard before entering the Tower, which lead Hon to submit to Zahard as a servant. You don't lose 10 out of 10 fights if there isn't a noticeable gap between two fighters. Furthermore, Hon doesn't seem to be the guy who would become someones servant if the gap was narrow and there is a chance to beat him.It's hard for me to imagine there being a gap between Jahad and Arie Hon/Koon Eduan.
since Data Eduan didn't look inferior to Jahad at all
Some people might refer to Eduan vs. Zahard, which by all accounts wasn't an all-out fight.
Others might say that the powergap got closer after they entered the Tower and learnt the use of Shinsoo, but this would imply that Zahard's powerlevel stagnated at some point while the others still improved, which doesn't make sense for the main antagonist which is Zahard.