Falco's Jab is definitely not F-tier. Its frame 2 so its able to break a ton of combos and just generally get the opponent off of him. It also has really good range for a jab. Its inability to connect properly (though I believe this is mitigated by rage) is an issue, but thats what makes this otherwise S-Rank Jab into a C-Rank one, not an F-Rank one.
Little Mac and ZSS have frame 1 jabs and it's not that common for them to break combos -- setups maybe, but not combos. Why? 'Cause they're light. Falco is light too which is why jab and Nair interrupts are rare let alone the fact that Nair doesn't start with hitboxes like Luigi or Mario's Nairs. The other thing is that ironically, Falco doesn't fall fast enough. Captain Falcon and Fox with Capt. also being heavy fall fast enough they can land and jab back against some characters, Falco being one, if people hesitate during their jabs. That's 5% from Falco and 9% or more from Capt. and Fox. Also, most characters don't do ground-only combos, they're likely to pop you into the air which means jab is no longer an option. At best, it's a panic button to try and do something against someone approaching you that Ftilt, Dtilt, and Reflector serve better as they're slightly slower, but have more range, more knockback, and except for Reflector, have about the same recovery. You can slap someone with jab 1, but after that, you're kind of screwed because of its average or high depending on how you look at it -- average for just any jab, but definitely high for a mixup jab -- recovery and low knockback.
By not connecting reliably and being able to do what almost every move in this game does and that's knock people back far enough to be safe, it fails at the most basic of things. That's not a C-tier jab let alone even a D-tier jab when the current listing of D-tier jabs all connect decently compared to Falco's or makes up by being tuned towards something which in Samus's case, is mixups, something Falco's can't do with its recovery. It has speed, it has range because Falco steps forward and leans in which is a double-edged sword because of how the developers animated it and because of its recovery leaving Falco posing waiting for someone to knock him out, it can ledge cancel rapid jab, a situational, but fine thing, and it's one of the few anti-air jabs in the game. Falco, Lucina, Marth, kind of Roy, and Ryu all have jabs that either start or end up high. Anti-air jab is great, but in Falco's case, it's not safe and it's not really reliable because what happens after it usually ends up with his opponent being able to jump away or even hitting him back. Lucina and Marth? They can possibly land a Ftilt or Side Smash if they don't choose to jab 2 to swat you away while Roy and Ryu with his heavy jab just swats you away which in Ryu's case, can end up killing you. Anyway, all of those, its frame 2 startup, its step in hit, and its high starting hitbox are "minor" things. The major things are what it does and compared to every jab in the game, it has nothing on them: it doesn't do the basic thing of being able to knock people back because it fails to connect into rapid jab and its finisher and it doesn't work a reliable mixup since you can jump out or hit him because of the recovery.
If it was "special" like Meta Knight, Pikachu, or Samus's and did something like jab 1 does 5%, jab 2 does 7%, rapid jab does 3% a pop, and rapid jab finisher does 5%, then sure, it not connecting reliably is fine when it does that ludicrous amount of damage for a jab. It would be the jab that fails at everything, except making your opponent fear taking a crapton of damage from his jab. Or something stupid like his rapid jab doesn't have a finisher, but if you only hit with the minimum amount of hits, it's -2 on-shield -- basically stealing SFV Rashid's unmashed light punch Spinning Mixer. The finisher is now his jab 3 now which doesn't connect like Samus's jab 2, so it's basically a mixup. Cool, somewhat safe shield pressure rapid jab and a frame 5 mixup jab 3 that goes alongside with Ftilt, Dtilt, Up Smash, Down Smash, dash attack grab, etc. Right now? Why would you be afraid of taking 3% to 5% when you can trade back double or just kill Falco when he jabs you? Captain Falcon, (Dr.) Mario, Fox, Jigglypuff, Little Mac, Luigi, Lucina, Marth, PAC-MAN, Roy, Ryu, Villager, probably Wario, and Yoshi certainly don't care. Why would you be afraid when you're just taking "glancing hits"? Jigglypuff, Kirby, Little Mac, Lucina, Marth, Sonic, and more can just jump out taking only 3% to 5%. You're really better off using Ftilt to do 9% with some knockback instead of hoping for a chance to mixup with jab. Moving away is a better option than using jab since while you're not doing damage, you're also not going to risk taking damage for picking one of the most basic freaking options in the game: jab.
