Yeah, what does "tanking" mean anyway. If you sit all your starters for the last 10 games or something like that, that would be clearly tanking (DAL did this recently). But I don't see shedding salary, in a season that your best player will miss the entire season (potentially), to avoid draconian penalties as tanking.
I see the moves as two tiers. Horford and Kornet found greener pastures. It made no sense to have Horford come back and play on a bad team and Kornet is still Kornet, a useful bench player who got paid. This kind of turnover is normal off season stuff.
The other tier is of course Holiday and Porzingis. Core players moved on from to get under the second apron. Purely for financial reasons. But is any of this "tanking"? We got nothing for Porzingis, not surprising due to his injury history. He may help ATL, he may not. And Simons for Holiday is not bad. Adding a young athletic player who can score a lot is not exactly tanking in my mind.