Reverse Flash and Grood aside I think the Smallville season 1 badies actually have a shot with folks that can read minds, become intangible, have pyrokinesis, disintegration touch, and heat feeding.
Also is the guy that stole Clark's powers allowed? That could certainly tip the scale in the Smallville teams favor
How fast was Clark in Season 1? I don't recall. I don't think he approached Flash level speeds. Reverse Flash can do a lot of damage phasing fists through people, especially with guys like Captain Cold and Heatwave keeping people busy with those guns. The guy that turned into poisonous gas may be difficult.
I took out the guy with Clark powers because I felt that would be too much for the Flash villains. If you feel otherwise, feel free to use him. I just want to try to balance it as much as possible.
Also was the guy that basically turned into the Hulk at night in the first season? Iirc he overpowered Clark easily
They'd essentially have to kill Clark instantly with the phasing trick in order for it to work since if he gets even one hit landed..he's kind of toast and Clark wasn't killed in a split second by the phaser putting a hand into his stomach.
Of course once you get past season one and to later seasons Clark could functionally laugh off anything Reverse Flash tried and then turn him to goo with the flick of a finger.