Probopass: Just... why do you have to wait so long to evolve this garbage? By the time you get back from Agate Probopass' only niche not better fulfilled by something else is being traded for a Togepi egg, and even then you're forced to fix the Railnet first to do that! If you want bulky paralysis, Stun Spore <insert bulky Grass or Bug type here> (hey, it's not like Probopass' defensive typing is any better lol). If you want suicide Rocks, literally any other SR 'mon with Sturdy is likely to have more offensive/defensive use and/or a stronger suicide move. If you want a Steel/Rock type because you like getting one-shot by a Fighting- or Ground-type sneezing on you, Aggron is actually pretty good.
Machamp: You get it late enough that you already have access to Conkeldurr(?), Hawlucha, Medicham, Chesnaught, and Emboar... which I'd argue are all better than Machamp in one way or another. No Guard Dynamicpunch is funny though.
Sceptile: Not as a starter choice (since I'm pretty sure Treecko is one of if not the fastest starter with an advantage vs. Julia and Florinia (Fury Cutter and resist to both Grass and Ground moves)), but from the event. It's a fast, specially offensive pure Grass-type, and sure, it gets some solid special moves (Giga Drain, Leaf Storm, Dragon Pulse, Hidden Power, etc.), and even a great ability in Unburden. But we don't have the Mega Stone yet (or the Mega Ring for that matter, though we'll probably get it fairly soon, within E17 or E18, since we're getting some stones atm), its typing defensively is meh (being noteworthy because of Electric, Ground, and Water resists) and its stats besides Speed and Sp.Atk aren't too great. Why does this come so dang late? Just stick to Lilligant for a specially offensive Grass sweeper. You don't need coverage when setting up to +6 in 3 bloody stats is made so easy. For a physical or mixed Grass sweeper, as odd as it sounds, Simisage. Acrobatics, Crunch, Seed Bomb, Shadow Claw, and idk probably some decent special moves too. There's also Roserade who has a 90 BP coverage move of any type due to Hidden Power + Technician, and also has other amazing moves like Venoshock, Toxic Spikes, Giga Drain, Leaf Storm, Extrasensory, etc.