An AI as smart as all the world's AI scientists would make progress faster than them (not saying how much faster or if it would foom) because

A it would be perfectly coordinated. If every AI researcher knew what every other was thinking about AI ideas would be tested and examined faster. Communication would be not a problem, whiteboards unnecessary

B I'm not sure if you meant smartness as Intelligence or as optimization power but an AI that had the combined intelligence of all the AI researchers would have MORE optimization power because this intelligence would not be held back by emotions, sleep, or human biases (except those accidentally built-in to the AI)

C Faster iteration: All the AI scientists can't actually test and run a change in the code of an AI because there's both no code and they don't have the supercomputer. Once you have an AI running on a computer it can implement good ideas or test ideas for goodness far faster and more empirically.

D It can do actual empiricism on AI mind, as opposed to what AI researchers now can do.

See also what Randaly said. For similar reasons as Robin Hanson's Emu Hell, a digital computer-bound mind will just be better at a lot of tasks than ones running in meat.