Not when Galactus was set up to be his most powerful ever by eating those 5 worlds, set up to be a big bomb?
Regular Thor once absorbed a blast that can destroy a galaxy and redirected it to a dying star and re-energized it.
Odin and Cosmic Powered Thor absorbed the power cosmic blasted by Galactus and used it against him. The fact that Galactus just recently absorbed 5 planets simply meant that Thor had more power to absorb and used against Galactus. All very plausible and reasonable, given Thor's ability and recent power levels.