I can agree that Fox isn't especially well equipped for abusing the ledge at higher levels of play, and in general he is more vulnerable to other high-tier character's off-stage game than they are to his, but I don't think he's in such a bad spot; he can stay off stage a lot longer and recover from farther away than most, so you can wait out a smash attack waiting for you on stage, and once fox grabs the ledge he has the same options everyone else has, plus a few extra tricks like ledge jump into shine/firefox/illusion. While some characters can follow him off stage with confidence, any attack that doesn't kill you leaves you with a fresh side-B and up-B, which is a lot more recovery power than most characters will have after hitting you.
With an opponent who knows how to play around your ledge game options, Fox does seem a bit weak, but if we are considering that level of play then we should also consider just how good fox can be when you hit those 1-frame punishes (an aspect of smash 4 I think is very under explored and under exploited). Ledge-snap Dsmash can kill at high% (or mid% w/ rage), and Utilt can convert into Uair or Bair in some scenarios (I haven't played with this too much on the ledge, but Utilt sets up a lot of things on stage, I would expect it to offer some of the same opportunities off stage)
Looking at punishing get-up options offers a lot of interesting possibilities. Fox might lack especially powerful lingering hit boxes, but his jab is super fast (Jab 1 has a hitbox on frame 2, IDK the numbers on his continuous jab, but it's fast), as is Utilt (hitbox on frame 3 according to Thinkaman's frame data spreadsheets), with these Fox can cover everything but ledge jumping on any character without a crazy deep ledge roll like Captain Falcon, both of these have amazing follow up options (double jab into Usmash is guaranteed at kill % on several characters, search youtube for "Fox's Double Jab Combo! (Wii U/3DS)" to see what else it can do). As for the ledge jump option, it's not that bad of a position for fox, they are down a jump so if you follow them with an aerial it could end the stock, if you stay where you are they can only land on one side of you since re-grabbing the ledge is basically suicide. Once my opponent ledge jumps I just prepare to shield their aerial, or attack if they try to land. If they go for the safe option and move across stage to reset to neutral, I usually send a few lasers their direction, if my attempts to ledge punish only result in 5% damage, slightly fresher moves, and a positional reset, I think it was still a profitable exchange.
I realize I've spend a lot of time talking about frame-perfect play and hypothesizing about situations with the assumption that the other player doesn't bait you into anything or simply beat you to the punch, this is a high-paced game and even a good player isn't guaranteed to win an exchange when the situation favors them. The important part is that Fox's bag of tricks is deep, and with good technical skills he can capitalize on just about any situation.
Now then, this has turned into a discussion about Fox's ledge game instead of his general stage preferences. Despite what my position on his ledge game may imply, I usually try to keep the game in the center of the stage, since I'm a very momentum based player and when the fight moves closer to the edge the opponent has more of a reason to back off and slow the game down. I know battlefield creates a lot of kill setups for fox, but I actually don't like fighting there as much, partially because I'm simply not as good at using platforms to my advantage as more experienced players are, and partially because I like to minimize the options I need to consider from my opponent at any given moment. I like FD, but against any opponent with projectiles I think it's a bit too much space to cover without any platforms, so I'd prefer town and city. When picking an omega stage, put some thought into the mild differences, like wall hanging. Also, be wary of stages with grass, I haven't done much testing, but I've heard that you slide less on stages like Windy Hill Zone, so you will have a hard time landing a fade-back into DACUS, my preferred center stage kill move. (also, avoid grassy stages against villager, his tree sprout thingy can be hard to spot).