I don't see how you can read this manga and think that its intended lesson on crossdressing is that, actually, no one should do it. The plain reading is that boys in dresses are cute, not boys in dresses are dangerous. Eru's not great here, but he hasn't hurt anybody and I really doubt he's about to start. He literally tells us that his shtick doesn't work, and he's just going to crush on Girly for a while.
You're bringing in a lot of culture war baggage that the author is probably only vaguely aware of. This story has already hopped out of any of the neat channels that we might have expected it to follow.
"this manga is transphobic and fetishizing" in no way translates to:
this manga is negative about crossdressing and is telling people not to
Now, if you think trans lives are just an advanced form of crossdressing then dear god you need to educate yourself. the fact the manga is letting you conflate the two demonstrates it is clearly is laundering transmisogyny under the guise of "we made them sexually appealing though!1!1!1!" it is quite the opposite i think this manga would prefer transgender identity never to exist or be invoked from how it already framed kitano, it would spoil the "joke" that Girly has won their affections, it spoils the fantasy thats laid bare by every boy-in-panty shot in here. The plain reading is they are almost exclusively sexualized either as a joke or purely out of fetishization. There was an immediate crass joke about genitalia being incompatible with womens clothing in the first few pages of this chapter, remember? I'm surprised you forgot!
and no trans issues arent a culture war hang-over, we bear no responsibility for the pivot and attack on all sides we have faced, it doesnt make our issues less relevant, especially given the history of trans fetishization and transmisogyny in animanga that has been criticized by japanese trans people.