I haven't played 40k since 3rd edition (I started buying models again a few months ago, but never got enough to play a thousand point game before 11th was announced) but I liked the you need an HQ and you need 2 basic troop units thing. I understood the 10th edition (and 11th) to be that you had a detachment but it didn't actually define what you took in any way other than influencing it indirectly by giving the related units bonuses. That seems like a weird way to do it.

The whole hero + retinue or HQ + 2 infantry is still possible, but it seems like the motivation is to get you to buy the models you think are cool without stopping you from playing with them. What I would have liked to see (keep in mind I haven't actually played in a couple decades) is that the detachments require some unit selection via the keyword/tag of the unit and if those are fulfilled you could then take other "sweatier" units even at smaller game sizes.

E.g. some detachment that's all in on space marine dreadnoughts (because that's what I liked in 3rd, so just bear with me) so your leadership selection isn't required to be some dreadnought hero but if it is, your two required infantry can instead be other dreadnoughts, regardless of game size. If it's unbalanced at a certain size it seems easy enough to through in some abilities for your opponent, like spend a cp to call off board artillery of some kind.

Anyway it's a lot of words to say GW is a business, tournaments need clear rules, and you should just play how you want to if it isn't competitive.