It seems like some of the issue is about how to handle damage and consequences for ranger and companion. I look at it like the Ranger and Companion are essentially one being with shared hit points, stats and screen time, making moves as usual, but with a huge difference in the fiction.
I ran another session of Dungeon World last night with an elven ranger, Alaria and her cougar Rik. During the first part of The Black Tide, Alaria sent Rik (a cougar) to spook the Templars' horses. I asked for a defy danger roll with Dex to avoid the attacks of the Templars. The results should impact the fictional situation of the Companion. So when she rolled a 5 against the Templars, Rik was surrounded and trapped by mounted knights bearing swords and calling for their spears. That seemed to work and lead to more interesting events.
For Hack and Slash, I applied damage or backlash to Rik in the fiction. The character doesn't have to mirror the damage to feel it. If Rik had broken a leg or something, Alaria would have felt the harm to her essence or however you conceive of Hit Points, but she wouldn't get a broken arm. If Alaria had taken a fatal wound during the adventure after any sort of mixed result, I'd always give her the option of having Rik take the hit and be killed, sparing her the damage just that once.
The cinematic style is certainly where I'm coming from. If you've got a bear companion, you have a BEAR with you. The things you can narrate with that ARE the benefit (or complication) you are looking for.The mechanical bonuses are minimal for balance, they are not the meat of a companion's benefits. A bear could rear up to push things over, see over a fence, or pull down a flimsy structure. A wild cat could leap over obstacles or climb trees in pursuit. A wolf understands teamwork and might even call in a pack of wolves to hunt prey or villains. These aren't limits or denials of the abilities of other critters. They are guides for you to focus the fiction.
Your particular animal companion's strengths are the guide to it's nature. Is your bear Burly and Intimidating, or Huge and Ferocious, or Calm with Keen Senses? NPCs are going to react to those tags very differently. The way the player narrates the fiction for their beast should change, too.
Hack and Slash, as written, is a tough case because, for example, a bear companion would seem to be stronger than most Rangers. Of course it is, and it can perform feats of strength and weight, as needed, in the fiction. But for dealing damage, the character's Strength and Damage and the Companion stats you chose are the measure of the class's mechanical effects in different situations, not a simulation of it's realistic benefits. All the realism or fantasy you want in your game happens in the fiction. If there are significant complications or issues you have, and that fit with the DM's AGENDA, turn them into adventures. What DOES a ranger do when his/her bear wants to hibernate? Find a potion to help? Grab a blanket and take a long nap? Or train it to resist the urge? That's for DM and player to decide, right? And if it doesn't sound fun or suggest some wondrous adventure, how about just letting it go?
I really enjoy running DW, but I agree some things could be clearer. In general I take some of the rules as a source of inspiration rather than clarity. And I'd mention again, that screen time is an important balancing factor for characters who can literally be in two places at once, more or less.
I'm burnt from DunDraCon. Happy dungeon-eering.