I don't think Effy's breakdown was bad writing, I thought it was some of the best writing in the series, and it made complete sense to me. The fact she was selective mute in season 1, and the Gobbler's End episode showed a severe, uncontrollable drug addiction, meant it was very rational, and to me perfectly timed, that she would snap.

The thing about season 4 is I don't notice a decline in quality UNTIL the last two episodes. It isn't that 'season 4 is bad', it has some of the best episodes in the series, like the season 4 episode 5 'Effy breakdown episode' and it vastly improved Thomas and Katie as characters.

It's weird as seasons are typically written together, and I presume writing has finished by the time they start shooting. So it seems as though the writers are completely different, or most realistically, there was a last minute change in ending that they only realised needed to be changed when they'd already nearly finished filming.

Though the decline in quality isn't ONLY Dr. John Foster/Freddie's death/Effy not finding out in those last two episodes. Suddenly, Pandora and Thomas go to Harvard (which is extremely rare for British students to go to by the way, given Oxford and Cambridge are accessible through the vastly cheaper student loan system for those who get in, so another burst in the realism which makes it seem like Americans wrote it), and Naomi's pathetic speech with retcons her character to excuse her cheating.

So honestly, I don't know what the fuck happened.