That would be hugely cost ineffective - the subscription service is cheaper than paying ~£10 to download the album.Alternatively you could have opened the iTunes Store on your phone, bought the album and had it downloaded in the same 20 seconds. You then own the music instead of perpetually just renting it.
Take the wedding playlist exercise... would you suggest I purchase digital copies of each song?
There is, in reality, no day-to-day advantage to owning copies in the current age. Likewise, Netflix etc and rental services makes owning films redundant (unless the cost for owning the film is nominal, or you watch the film again and again, you may as well just rent).
If you think it’s a material risk that Apple will pull Apple Music, or increase prices, then don’t subscribe. In the meantime, I will take that risk and enjoy unlimited music conveniently at a decent price.