Obviously because it means I have to spend less resources to play the decks I want?
I didn't really address this because the resource gain is entirely subjective, if you don't have time, then use money, if you don't have money use time.
I also didn't want to mention it, but expecting to play whatever deck you want, is a very tall order - by design. There's no meaningful difference between "being able to play all the decks I want" and "wanting every card".
Money is the fastest and you've got to pay for the solo content anyway. So how is the solo content objectively a better way of using resources? It isn't, it costs money - or time.
If the value for doing the solo content is better than just buying the packs, it's not really optional.
Yes it is optional, unless you're OCD or can't control yourself. It's entirely optional, because it nets you nothing special. Whether you play the solo content or not, you get the same cardpacks as the ones who do play it.
That means: optional. How can it be objectively better, since it too costs either time or money? It's entirely subjective.
If it's not then great, but why even have the content then
Because you're not the arbiter of content?
Because people asked for it?
Because ActiBlizz want's more things to sell?
Not sure if serious, indeed.