Yeah I think onslaught at his best will have the powers of franklins who can warp reality and create a pocket universe etc and he is on par with the celestials etc so onslaught will probably win . Unless Odin uses a plot device or some amp with the Odin force ,he will probably make the battle more competitive for onslaught . Maybe rkt could contain onslaught ...
been done before use search function. Basically it came down to how handy Onslaught was with Franklin's abilities. He showed himself on last showing unable to comprehend the full scope of Franklin's abilities. Not even CIS that did him in but more along the lines he just didn't have time to explore the potential. Odin beats Onslaught due to the fact that Onslaught is unfamiliar with Franklin's powers so his ability to use them effectively is in question.