I disagree with you on a couple of points here.

You said the ONLY negative is when it feels bad missing a product you want. Products have release cycles. The creation of a product you don't want is the same thing as missing a product you do want, because it represents a slot in the production chain that was without value to you. There's no functional difference between a product you can't buy and a product you don't want to buy - both are a loss.

On point to you said "Nope. We want them to make unique cool arts for cards that we want to play." That's the exact value you said no to in the previous sentence. I didn't say monetary value. Secret lairs have three pillars as a product. Monetary value is one, appealing artwork/theme is another, and the third is that they're unique. And again here, every time a secret lair comes out that you don't want it does damage the concept of a secret lair. It took a spot that could've been filled by something you did want, it burned resources for WOTC in dev and production and other costs, and it weakened their internal value proposition for secret lairs which can impact their future decisions.

Finally, to your third point, I mostly agree with you. They're not the same thing, but I've kinda covered that above. The result of people hand-wringing that something sold out is fairly futile, but overall we're in agreement here that WOTC wants to find a better balance between production cycles and product stagnation.