Whilst Bruce Lee did have feats that bordered superhuman, they weren't on the level of low tier DB characters, such as Yamcha smacking Goku through several large rocks, 21st TB Goku moving a giant boulder with help from Kuririn, etc. Bruce also believed that challenging other fighters in their preferred area would give them an edge, such as feeling Muhammed Ali would have an advantage over him in a boxing match, so he's in no way capable of taking down Giran.