OKC was okay to match because the cap went way up. They (stupidly) didn't anticipate the rising revenues and cap. They were so paranoid about the luxury tax that they wrecked a potential dynasty over what might have been a very brief and very small luxury tax bill.
The dumbest thing about that Harden mess is that they still had him on his rookie deal for another full season AND then they'd have his bird rights as a restricted free agent where no team could offer him more than 4 years, 58 million. Instead they bet on Harden not being a legit star and that the assets Houston sent over were more than just a bunch of chicken feed.
They screwed up royal.