Most trans men and women are indistinguishable with cis men and women now. Most of the public's awareness of trans people is based on media where trans women are played by cis men, which is deeply offensive and ends up getting trans women murdered.
I hate the idea that this reasoning would be an excuse to just cast a cis women to play a trans woman and pushes the idea that all women are supposed to look exactly the same.
I would presume that the indistinguishability would be variable, based on where the person is in the process of transitioning. I would like to see us get to the point where it doesn't matter what someone looks like relative to their identified gender. Because to me, it doesnt. A person is a person, regardless of all of that.
I too don't believe that producers and casting directors should cast a cis woman to play a trans woman... that makes no sense to me other than they think they are going for the aesthetic, which misses all of the points entirely and is insulting to everyone.