Most big AAA games get downgraded by release (though certain other publishers games' actually improve visually closer to release), it's just a fact of the industry. I don't think it's intentionally misleading the consumer, just the reality of having to ship a bug-free game with a decent performance. I'm obviously not a developer but I suspect it's much easier/makes more sense to aim high then dial back if need be. Oh and I really can't see this game not being worth £50, it'll be full of content, and still looks beautiful IMO.
The DLC thing is annoying but it's the reality of games being cheaper than they've ever been, whilst being 100x more complex than back in the day. The timing of it is ridiculous though, that is inexcusable.