Time changes all things; and in the case of Hard Knocks it is Wolverine who has brought the winds of change to this card. While indeed cards like Tackle are more powerful overall; that has a pre-requisite required to unlock the damage in addition to the stun. If Wolverine plays that card using Wolverine's Claws he will only deal the stun; and while a stun for three hit points and a card is not the worst deal in the world, it's also not really good enough to include in most decks. So, instead let us look at Hard Knocks through the lens of the Captain Canada.
When used in a Protection aspect deck; Hard Knocks provides a way to utilise Wolverine's Claws defensively; as their activation is a Hero Action for an Attack Event you cannot funnel many of Protection's best defensive cards through it. Hard Knocks offers a way by allowing you to spend one card from hand (the Hard Knocks), exhaust the claws, lose three hit points and gain a Tough status card by defeating a minion with 4 or less health even if that minion has tough (because Wolverine's Claws gives this attack piercing). That's a huge deal for any Protection Wolverine in solo and it is also very relevant in multiplayer as you can both deal with a threat attacking one of your team mates plus take an attack without losing more any more hit points outside of the three already spent. Wolverine might have inbuilt healing, but Tough gives that Healing Factor regeneration a bit of time to recover from low health.
When we are not just leaning into Jimmy's decks Hard Knocks has a lower ceiling, but the floor for this card is huge in any hero who has great on board resource generation, ways of boosting its damage like Gambit or loves to have toughness like Colossus. Protection Thor is another place where this card has a great home because of Thor's preference for fighting minions with "Have at thee!". In the opposite style Drax likes this card also because he can use the tough status to gain vengeance counters without losing hit points. Last of all heroes with triple resource cards like Captain Marvel and Hulk are able to play this card for a net two cards instead of three or four.
Some other card to card synergies in Protection include Bait and Switch which will let you turn that toughness card into four damage right the villain's keister; Unflappable which will be triggered when you take no damage (thanks to tough) and classic Protection upgrades like Electrostatic Armor
All of this makes Hard Knocks a staple that you should pull out when you are starting to build a Protection deck and you should always seriously consider keeping it in the final build, cutting it only when it is clear that the deck is not needing an injection in the minion punching direction.
The Best Defense… is a good offense indeed.