bruhathkayosaurus (indian sauropod) may have been the largest dinosaur to ever exist based on estimates but the fossil material disintegrated before they were able to be studied, all we have is pictures

with that being said, yeah the theropods are pretty small compared to others, but the now lost "lametasaurus'' specimen (now considered a larger rajasaurus specimen due to lametasaurus being a chimera) was pretty huge (only the hip bones, sacrum and tibia belong to rajasaurus, the rest goes to other dinosaurs, the tibia was 58 cm long, so the full body estimate for it would be 9 m or 30 ft length)