I try and avoid most of the reffing arguments as they've got pretty much an impossible job with the complexity and speed of the game. Some of the noise around it from teams and fans alike has been a bit footballish which is a shame.
No harm in discussing decisions as it's part of the game but bias between sides or tiers is wide of the mark in my view. Until refs are replaced by AI you're dealing with humans and all their fallibilities. While you'd like to see 100% uniformity, all you can realistically hope for is refs being consistent over the course of any given match.
Yeah, I think the closest you can get to bias from ref.s is teams being better at adapting their play to the ref - which is a skill, and one I'm happy to accept that some teams are better than others at. England, for example, are historically terrible at it; but probably better than just about any tier 2 country, purely through having greater access to the world class referees - both for club and country.
Cheating is the longest, and proudest tradition in rugby - hell the game was invented by someone cheating at football!
"It's only illegal if the ref notices" has been a cry in rugby for longer than I've been watching the game (40-odd years).
Tonnes is missed by ref.s, because every player is cheating just as much as they think they can get away with. Generally, these things even out - it's the clear and obvious mistakes (and warnings given, but ignored) that grate on the nerves, but even then, if the ref is consistently making that same mistake, then it's your job as a player to exploit that.
And it always feels unfair to the team who fails to adapt.
ETA: I should also add the language barrier - with more matey ref.s who are warning and coaching players, rather than blowing the whistle and then explaining - if there's a language barrier between the ref and the player, then there's a delay in the instruction being registered, and a slower-to-respond player is more likely to get the whistle blown against them. That goes for not understanding the instruction and for not understanding who the ref is speaking to. I'd say this is also a problem increased when the player feels they're in the right - you still have to obey the ref, but you also have to know that the ref disagrees with you.