Honestly, this resembles Jackie Chun vs Goku for me. They are about the same level, but Goku is just more skilled, determined, etc.
Round 1 Goku beats Tien in their first round fair and square. But it's not really a power thing, just a skill issue from what I can see.
Round 2 is Goku not falling for the Solar Flare and hitting Tien while he's open. Tien counters while Goku is slacking giving the glasses back.
Round 3 Chaozu is paralyzing Goku.
Round 4 Tien's 4 arms vs Goku's 8. Now this is the round where you can suggest a large gap. Goku someone is able to speed past Tien's advantage and gives Tien a literal whooping. I still can't help it comes down to technique here and although Goku doesn't have 8 arms in actuality, it's pretty much like he does.
All in all, it's the same as Jackie Chun vs Goku in the 21st Budokai. Goku is too tough to beat head on, so the opponent goes to tactics which Goku uses better than them and gets the advantage.
So all in all, a small gap is still doable in my book. I think Goku is just a nightmare to deal with at equal levels, he seems to put a whooping on everyone with powers in close proximity to him. I think Roshi, Gohan, Tien and Piccolo can all agree with that.