I'm almost up to date with the edem zero manga and I dont remember the fan service ruining the story unless you are very averse to fan service as a whole. Mashima does it a lot, true, and bless his heart for it, but its better than Fairy tail imo since at least the main girl, who also gets the most fan service, is actually useful as fuck and the most broken character together with the MC, and not just a piece of meat like Lucy was for 90% of the series
Same goes for the other main girls
but dont get me wrong, Eden zero is EXTREMELY mediocre, it takes too much stuff from one piece(more than fairy tail in fact), theres a bunch of rehashed designs and even its original stuff is lacking a lot of depth to it, but I wouldnt call it straight up trash like I would fairy tail or seven deadly sins (towards the end). Also you fucked up by watching the anime, the manga at least has some really nice art from time to time while from what I've seen from the anime its all very mediocre