This should be a feature, as simple as that. Please please please add this. It was a request since the dawn of time when ACF started and there are various topics and posts on it and the feature request was marked as solved because someone came up with a code fix.
However that shouldn’t be needed. It should be possible to do it in the ACF UI.
It’s incredibly inconsistent to have a textarea field allowing a height setting and not the WYSIWYG field.
Please do the decent thing and get this tiny change implemented, it will save so much time!
Requests really need to go to the devs, they don’t frequent this forum. You can use the contact form or you can open a ticket in your account.