The fish does still taste a bit battery if that makes sense, it tastes completely different to getting a piece of none battered fish and cooking it in the oven anyway. I've done this in the past but it really depends on what mood your in as I've also planned on doing this but then ended up eating the batter anyway lol.
A small portion of chips is 17.5 syns as well, so if you really fancy them you could borrow some syns from other days, I'm not sure how small a portion slimming world mean though, the chippies around here serve massive portions, my MIL couldn't believe it when she came up to visit last she ordered from out chippy/Chinese and ordered a portion of chips on top of her meal (we warned her it was all big portions but she didn't believe how big until she saw it)