I just checked, and the lawsuit did start in 2020. So the timeline is;
- H&W started writing new books, with WotC's permission.
- WotC started developing Dragonlance, H&W sues WotC. Which happens first isn't clear.
- H&W dismiss lawsuit.
- WotC completes and announces Dragonlance for 5E.
So the lawsuit and the development started roughly at the same time. To me, it looks like if there was any chance of getting H&W's input on Dragonlance, it went up in smoke when they sued. I know Hickman consulted for Curse of Strahd, so I wouldn't be surprised if WotC started DL development and intended to get input, then the lawsuit started and they decided "Naw let's not, let's do it ourselves only."