Hanley who left Wigan for more money at Leeds? Offiah who according to John Monie in his autobiography almost signed for Leeds on more money than Wigan were offering?
The trouble is you are being awfully selective with your recollection. Widnes won the league twice in the late 80s with an extremely good team and other clubs also had stars like Schofield, Crooks, Ward etc. Wigan by no means signed them all and always had a fair smattering of players that would be considered average at other clubs or journeymen. The typical starting lineups often included the likes of Mather, Cowie, Panapa, McGinty etc. Before that you may have had the likes of Preston, Myers, Byrne etc. The likes of Hampson, Preston and Mather were nobodies even in RU. Then there were all the homegrown Wigan players who were a core part of these teams.
Indeed Wigan only won the league on points difference at times in the 1990s. For a team that was supposedly the only full time team and that signed all the best English and Aussie players it seems odd that this could be the case.