Drill shine, while powerful, has been proven to be very SDI'able. Some foxes still do it often, but are mostly unaware or inexperienced with players with good smash DI, or simply do it as a mixup here and there. Nowadays the strat vs peach has been changing a lot thanks to the defensive power of peach, and good foxes tend to play more campy than usual. This is just assuming that the player skill level is equal such that the fox can't just overwhelm peach in the neutral game and upsmash her for days.
The reason peach struggles so much vs fox is mostly because fox can outrun peach, laser her during low %s and fish out kills with bair,uair or upsmash (especially upthrow uair which can kill peach starting at around 50-70% depending on stages, IF the peach doesnt SDI the upair). On top of that, he has very easy waveshine strings unless the peach smash DI's those, and even then the fox may be able to follow up and finish with an upsmash. Good peaches should be able to know how to avoid the shine spikes, but those are as much of a threat to peach as they are to marth or sheik. Peach heavily relies on zoning out the fox and getting as much punish % as she can off of a few hits, but due to the speed disadvantage, it may be pretty hard for peach to land those hits safely.
Peach's punish game is so strong that 1 hit is potentially a stock vs spacies. Armada shows that very often as he climbs his way to grand finals. However a fox with a good presence of mind knows how to SDI some of the early combos, and knows that he must keep the lasers on peach, and slowly build up the % until the fox can go for upthrow uair kills or raw bair into edgeguards. It's a volatile matchup for sure if the peach is fast, just like the marth matchup. But due to peach's naturally slow movement, it takes a good player to make her fast, and a lot of peaches tend to lose the match simply because the fox is much much faster and dictates the rhythm of the match.
In the fox's mindset, the game plan is to shoot lasers, get dmg whenever peach lets him (let it be shffl aerials + waveshines or whatnot) and get her to 60-70% where the fox can finish the kill with an upthrow upair or upsmash at around 90%. Beyond that he may be able to simply bair peach off the stage and keep edgeguarding until she dies.
