Interesting question.
Bad QC is definitely one, but my biggest one is unimaginative representations of characters with someone else's mould. Sometimes reusing a mould works really well, ie Kup to G2 Electro, Springer to Sandstorm, Aramda Starscream to Jhiaxus and Scourge to Senator Ratbat for example. Others, like Gen Legends Megatron to Warpath, Gen Bee to Nightbeat and dare I say it, Optimus Prime to White Op-err Ultra Magnus etc are just boring, and not quite right, at least in my opinion.
But to discuss your point 2, that's quite an interesting one. Sometimes deluxe is all you need, a large percentage of my collection are deluxe figures, from quite simple ones (like the Night/Bee mould) to downright annoying (WFC Bee - which just got auto-corrected to "WTF Bee." Not too wrong there).
Having said that, I've got a number of voyagers too, because they were either the best/only representation of that particular character. Now ones like Gen Spring/Storm and ROTF Bludgeon have some complexity, they're relatively intuitive (more than I can say for WFC Bee,) while others, like Gen Brainstorm, FOC Soundwave, CW Prime/Master & Silverbolt and Universe Inferno are pretty simple figures. Brainstorm especially is quite simple compared to even Gen Skids or Kup. Even Titan Metroplex and Leader Megatron are simple compared to ROTF Lockdown and Gen Straxus.
So while I understand your point, these days size doesn't neccessarily mean more complex (in some cases it's the opposite) - don't be afraid just 'cause it's a little bigger

(in before any "That's what she said!" jokes)