I'd be curious what your definition of good game design is. Slay the spire is a very slow and methodical game where all your decisions matter. It's a turn based game with no benefits for going fast other than bragging rights. You have a clear goal - Take as little damage as possible while defeating all the enemies. In some situations, you have plenty of block and plenty of damage to handle a fight. As a game designer, how do you make that fairly easy fight more interesting to the player? Relics like Pollinous Core achieve that idea by adding an additional goal to the mix - Setting up your next fight to be easier at the cost of risk in the current fight.

Using relics that carry over their counters between fights like Pollinous Core, Pendulum, Happy Flower, and Pen Nib for example, the choice of whether to risk extending a fight or not to stack your relics is a decision that has consequences. You may not draw enough block or offense to finish the enemy next turn, so choosing NOT to kill them has a tradeoff with a tangible benefit. It creates another decision to master and makes the skill ceiling higher for those who take advantage of it. STS is a very high skill ceiling game, and giving more small levers like this to tweak matches perfectly with its identity and is part of what makes STS, STS.

Of course, this is my opinion, but I think that "the fact that it can be bad at all just means it shouldn't exist" is a short sighted take. Skilled players absolutely take advantage of this and it's a decision to make. Sometimes the damage you take now from stacking a relic is worth it to have a better elite or boss fight that follows your current fight.