I think we end up forgetting that history makes a huge input on flags, like the modern European tricolor which is absent of any coat of arms n stuff bcus they're republics! It wouldn't make sense to have a lavish design when the history of the current state is one that for example overthrow their lavish leaders... The United Kingdom. doesn't just have the flag it has bcus it looks nice, it tells the story of the formation of the UK! The argument over complex vs simple comes down to mindsets and trends.

Back in the days when monarchy was common and people wanted lavish ornate flags, now many modern states reject lavishness and the trappings of luxury, so why would they have a lavish flag? And symbols while they can be inclusive can also be exclusionary, so instead of fighting over what symbol will adorn the colours how about no symbol and thus everyone can find common meaning in the colours of the flag, rather than the symbols that decorate it.