Just stop. There is no mechanical or thermal restriction here. This is the way transmission coolers work on almost every car you can think of. Mercedes specified a short drain interval either because they are, what's your phrase? OCD, or because the transmission has some specific issue they felt needed to be addressed. Or, the explanation is that as with so many other things, this happened to be prior art in the Mercedes design room and nobody thought it was important enough to challenge. I'd be curious if anyone has extended their drain intervals, and what the experience was, but that's another thread.