Since you said no grinding, there's not a lot to say, but:
Instead of 2 Fire moves, you could give Magmar Brick Break. I also dislike relying on unstable things like Confusion, so I'd swap Confuse Ray for maybe Sunny Day, especially if your Venusaur has Chlorophyl, which is easy to change to with Ability Capsules.
Why doesn't Rhyhorn have Earhtquake instead of Drill Run? Also I'd say Chip Away would be more useful than Take Down in certain scenarios at the cost of a little power. Your team is not the fastest, so Bulldoze could give some nice support as well.
Standard Gardevoir. I'd say keep Shadow Ball and Calm Mind, but if you want to change those, Hidden Power and Magical Leaf are your best options if you won't breed. ML could be useful because you only have one Pokemon to hit Water types super-effectively with, HP's usefulness depends on what you get.
Sleep only last up to 3 turns, so I believe there are more useful moves. You could use Double Edge to reduce the number of foes you don't hit at least neutrally from 334 to 60. With Synthesis and Leech Seed, the Recoil should hardly matter.
If you give Magmar Sunny Day, swap Razor Leaf for Solar Beam. If not, Petal Blizard is better than Razor Leaf. Only the PP is worse.
It hurts me to look at a Scrafty like that. It can breed for Zen Headbutt, Dragon Dance, Drain Punch+Fake Out or the 3 Elemental Punches. Buuuuut you said no grinding and/or breeding, too bad.
The Obsidia Dept Store has an item that improves the holders accuracy should the foe outspeed him. With it, HJK has 99%-ish accuracy. Facade could be more useful than Strength, especialy should you happen to get burned. After all we don't know when it's Charlotte's turn. Other than that, uhhh....Head Smash and maybe Scary Face are useful/usable. Since you don't have Dragon Dance, you don't have the speed to sweep, so Moxie may not be that great. It's better than Shed Skin IMO, but Intimidate would be most useful.
Standard Gyarados. Although the Circus has a tutor for the move Bounce. Dunno if it learns it through tutoring in Reborn the same way it did in gen 5, but try your luck.
As for team options, I'd say swap Rhyhorn for Crustle, especially because Shell Smash is a thing. You could breed it with Shuckle for Earthquake, just saying.
Aaaand Swaping Magmar for a Zubat/Golbat/Crobat. It gives you a few things you don't have, most importantly ways to hit Fighting and Fairy types super effectivelly, as well as some actual speed. It can be caught in Aventurine Cave at level 50-ish, and with a friend Ball, you'll get it evolved in no time.
Welp, that's all I've got, without breeding, grinding or what have you. Just a trip to the Dept. Store, using some Heart Scale and getting a new member is all I have to recommend.
EDIT:There's also Mienshao. Bounce, U-Turn (+Regenerator), HJK, Fake Out would be a good non-bred set.