Not sure why you're saying raiding is worst than other expansions. There is no reason why you'd say that. Emerald nightmare is what it is. Nothing remarkable but a cool concept. Trial of valor is a short 3 bosses raid, but nighthold is beautiful. It fits well in the world around it and the bosses are entertaining. Not sure why you'd consider it WAY WORSE than previous expansions.
Also not sure where do you see rehashed material in legion apart from Dalaran.
In terms of systems in place, it allows for a lot of variety at end game, with m+ allowing from an unprecedented way of experiencing raiding "progression". Votw tyrannical +16, second boss felt like a raid. Wiped on it until we got the fight and just kept on going till we nailed it.That's good design right there. The new lfg system, the one in place for m+ is great. It's not as random as lfr or lfg, you can talk to people and see if they're normal or disturbed before starting a run. I've been adding tons of people on my friend list. Hasn't happened since TBC. I regularly meet them again and organise m+ runs with people I've met before.
Overall there's a good balance of everything. It's a great expansion.