Well unless you run all 2-3drops or all big mobs, Argent Commanders are gonna kill something when they're played anyway. At least the Azure Drake drew a card, which beats a lot of other stuff. There's also the lack of good 5s in a lot of classes that do run drakes. Like Druids don't need to run drakes cause druid of the claw is fucking awesome, but for some other classes there's Sylvanas and Azure Drake pretty much. Can run tiger or the 4/4 2/2 I guess instead, not a big fan of either. Tiger might not be too bad, avoids flamestrike, can't be soulfired/power overwhelming/evisc/whatever until you attack and since it's 5/5 can often 2 for 1 or at least take a card and force hero power next turn.
Thing is when it's really lategame, like turn 10+, drawing an Azure Drake is one of the best draw since you can play it for a fairly good body and draw again to potentially play one more. That's when Azure Drake is best I think, I agree on turn 5 it's not really that great, it dies to previous turn 4 drops and potentially turn 3 drops with buffs and dies instantly to turn 6 commander too if you're second. Has some small synergy with rogue decks where you can backstab on the same turn to use the spellpower but that's about it.
On brewmaster, I really like them when I play arena, often get more value than a standard card. The main issue is when you draw them and you don't have a battlecry on the board but other mobs that are too expensive to be played at the same time, so you can't actually even play the card at all without weakening your board. A single one to surprise people could be good though I guess, like black knight an ancient of war, druid play his second ancient of war, panda the black knight and kill it again, that's like gg. Can also be used as a heal on the bigger mobs if they're not killed in one turn, like Rag taking some mobs as a setup for a next turn kill.