In DBS the Grand Priest was going to have Merus erased because he was about to violate the "Angel Code" by fighting at full power against Goku. And then the GP goes on a rant about how Angels must always stay neutral and not interfere in mortal affairs etc.
Yet he allows Whis to keep doing his thing even though Whis-
rewound time to save the earth.
rewound time to save Gowasu.
resurrected Frieza after the TOP.
continuously trains Goku and Vegeta.
etc.
So why is it ok for Whis to interfere in mortal affairs like that multiple times, but when Merus does it once he gets killed?
Presumably these 'alterations' were acceptable because Beerus ok'd them... And Whis' entire role as an Angel revolves around making Beerus happy.
Whis has never come remotely close to using his full power against Goku and Vegeta during their training sessions. Evidently training while holding back is fine, but an Angel using their full power constitutes a proper battle, which is forbidden(Daishinkan himself acknowledged this.)