Feige said that. He also said that Coogler will be turning in his outline (this was a month ago) probably around now or if he hasn't got it already. We've got history of him writing a script from August to January with the 1st movie.
If he can't finish the script in time....then move the date
Studios do it all the time. Marvel has changed release dates before.
Oh and I forgot Jon Watts made Homecoming in 2017 and Far From Home in 2019.
Its not a big deal to me....just healthy discussion
If Coogler wants to do another project thats all good. Who wouldn't want to see more work from an excellent director. Thats a legit reason to wait on him. However, there has been no movement on that other movie. MBJ has moved on to other projects as well.
I just think the simple answer is they didn't want Doctor Strange or Thor to go 5 years (6 for Strange) since they're first film (we don't count the first two Thor movies.)