I found it funny that you took 2 stocks off his sheik, but got 4 stocked by his fox lol. For me it's usually the opposite, I have extreme difficulty fighting sheik unless I get alooooot of cg's or d-tilt gimps.
I agree that cc'ing GW's d-tilt at low percentage is generally a good idea, unless we're talking about peach's d-smash or falco d-air/shine pillaring.
I also agree that n-air out of shield is definitely too slow. Though I like to use gw's n-air if i'm predicting a sidestep-dodge, cuz it punishes that really well (especially spacies).
F-air out of shield can be too slow, but if you use a retreating f-air out of shield, It could space you enough to release you from shield pressure.
I actually like to use full-jump d-airs out of shield for two reasons:
1. if they jump after you, chances are their aerial won't out prioritize gw's d-air
2. G&W's full jump d-air auto cancels, so you won't necessarily have to land right next to your opponent when the d-air is over. You can wavedash, 2nd jump, airdodge, etc. after it auto cancels. Also, a lot of players don't know about the d-air's second hit, just sayin lol.
However against Peach, I really don't think G&W can do anything about her shield pressure. Nearly all of her aerials shield stab G&W, usually in 1, maybe 2 hits...so stupid. But maybe an up-b or wavedash out of shield can help you escape from a peach if somehow your shield absorbs a hit without getting shield stabbed. I need to test out up-b out of shield, but I agree that that's also very stage dependent (don't wanna be doing that on FD >_>). You could do a retreating f-air out shield, but you have to pray she doesn't jab you first. Peach is a *****.