Zihi seems more universally applicable, and will probably have a longer meta life than Hakkar. Once Waggle rotates, Hakkar might find quite a bit more trouble finding a deck. Mechathun seems better for an otk style deck if that's what you want.
Seconded Baku. Velen is likely dead post rotation due to all the resurrection cards rotating out. Baku will be better for longer, and if you have any interest in wild it will be permanently powerful. It's also more likely to be nerfed in my opinion, so could be a free craft.
Tier One are meta defining legendaries, and as a result is subject to a lot of movement regarding what deck is working at what time.
Tier Two are cards with high winrates but not essential to any deck in the meta, they're seen more as 'tech' thus the name.
Tier Three are cards that don't have a home, but are decent nonetheless.
Tier Four are cards that have a home in typically low winrate decks. The fact that they have a home means they aren't trash.
Tier Five are cards with low winrates and no decks associated with them.
At least that's how I consider it. Perhaps you should take this list as a guideline, a pretty accurate one at that despite your complaints.
Bear in mind as well you attack Garrosh for it's low playrate, which you back up with personal anecdote, whereas Slyde is arguing from a winrate perspective. So much for objectivity.
On a final note, consider reading disclaimers:
'Disclaimer: A tier list like this can never please everyone; the meta game is dynamic. If you think a card is in the wrong tier, please explain and provide links to deck lists or other data to support your claim.'