I dont recall that DE directly said why new war and duviri Paradox is delayed. This reasoning that they can't release new war or duviri paradox because of covid seems maid up by Fans without DE ever confirming this.
Original they announced that new war release for end of 2019 so Covid can't be the only reason for the delays.
Squad Link changed to the system with Scarlet Spear, DE said that the original design of Squad link didn't work in playtest.
Duviri Paradox was always a new open world this is the description from the Reveal Trailer on youtube: