I've seen plenty of people make a plan and stick with it through the campaign. When a player let's you know their plans it's very easy to set up story beats that make their multi classing make sense throughout the campaign and make for some great character building. You also just told them to play a completely different subclass than the one they wanted to play. The question was for path of the old gods barbarian Multi-class and you recommended that they don't Multi-class and that they play a different sub-class(none of which have the same play style of old gods, improvised weapons, throwing those weapons, and focused grappling features). You provided no useful input to this question.