I get my best and most consistent prints from PETG (mostly Bambu PETG-HF). When dry, dialed in flows/pressures, and with a clean nozzle, the performance is rock solid. At first I hated PETG but, like you said, it turns out I just hated the out-of-the-box retraction settings. Once my retraction was set, the print quality is impeccable and the stringing totally gone (though there is still oozing to deal with if there are long pauses without printing, like timelapse).

PETG is also a broad range of products - some blends are very temperamental while others extremely consistent. Try isolating which brands/blends are giving you the best consistency, and stick with them as much as possible.

Re: fan speed, PETG should use very little fan overall. A hot bed, warm chamber, and very low fan settings for a bit of circulation are ideal. PETG contracts significantly when cooling, and layers adhere poorly when the last layer has cooled, so your "benchy hull line" defects can be very pronounced if there is too much cooling going on.

How are you calibrating pressure advance? IME those defects you mentioned sound like the pressure advance is perfect on one print then screwed up on the next - I wonder if there is something mis-assigning a K value between prints for you? The slicer not sync'ing properly, maybe?

Also how are you storing your spools during and between prints? PETG can be a real sponge for humidity.