The money argument is IMHO not super strong, here as that Mac depreciates more per month than the subscription they want to avoid.

There may be other reasons to go local, but I would say that the proposed way is not cost effective.

There's also a fairly large risk that this HW may be sufficient now, but will be too small in not too long. So there is a large financial risk built into this approach.

The article proposes using smaller/less capable models locally. But this argument also applies to online tools! If we use less capable tools even the $20/mo subscriptions won't hit their limit.