I have played with and DM'd a munchkin - they sucked the life out of the game for the other players, and constantly butted heads about rules/interpretation. It was a miserable experience and NOT about roleplaying. Munchkins (and higher end powergamers) can seldom justify their class building in a way that is consistent with the campaign or world and their place in it. The obsession with dipping into N classes (usually with no clear world/story justification) is an example of that and why I dislike that stye of play. Being 'the best" is all that matters to some, regardless of how it impacts on others. Well, the munchkin died (a little too much arrogance and they bit off more than they could chew) but I find such players toxic - and have been fortunate enough to play with groups later who are more focused on the RP aspects. Simply blaming the other players or DM is pretty arrogant, but to be expected from people with a strong sense of entitlement.
So you have an issue with dips?
Dips are a great way of further dialing in the character fantasy and are fun mechanically.
Is a barb dip for a moon druid strong? Yes. Does it help you fulfill the ideal of playing a primal guardian of nature? Also yes.
Also many if not most lore characters are multiclassed so claiming it breaks rp is pretty silly.
If its your hombrew world that's you prerogative but you should let players know all this in session zero so you bother arnt play a game neither like.
