I don't agree with this; while I don't think 40k or any GW game should be heavily designed for tournaments, balance is very important as without it we get armies that people are reluctant to play because it's more difficult to just enjoy pick-up games when your army is riddled with disadvantages. Even in a friendly/casual environment this can be a problem, particularly if you're not planning a game in advance and decide to take you 1,500 points of Tyranids to play in store and end up against 1,500 points of Grey Knights, for example. GW have been showing in 8th edition fantasy that they're capable of producing army books with good internal balance, that are also balanced well against other 8th edition books. 8th edition is still far from perfect, but when it came out it levelled the playing field and the books have only supported this.
40k's current set of codices are pretty disgraceful in balance terms, and it makes it difficult to hype up an army that's difficult to play because it's underpowered. For players that care more about the modelling and painting that's not such a big deal, but most people want to play the game at some point, and even playing casually a lack of balance in the rules or codices does hurt enjoyment of a game.
You could have the clearest possible rules in the world, but they won't be fun if there isn't at least
some competitive balance. Take this as a rules example "Space Marines always win"; couldn't be simpler, but I don't think it'd make for fun games
