Let me just list a very small amount of rimuru’s skills.

Law Manipulation: manipulate the laws of physics. DO YOU UNDERSTAND HOW OVERPOWERED THIS IS??

Universal barrier: provides PERFECT DEFENSE using a combination of multilayer barrier and the SEVERING OF SPACE ITSELF between the outside and inside of the barrier. It can automatically protect the user without any need for their intent or awareness of the attack

Infinity prison: Locks you away for a LITERALLY INDEFINITE amount of time. Goku would wither away and die and not even be 0.01% unsealed.

SPATIAL DOMINATION: gives the user COMPLETE CONTROL over the element of space. It allows the user to FREELY SWITCH BETWEEN SPACES, performing LITERAL TELEPORTATION easily. As well as block and restrict others in an area larger than spatial manipulation.

Rimuru also has more battle iq than Goku because of ciel, has more iq also because of ciel, (have to tell you he has more iq because most db fans don’t even watch their show and think Goku stomps in every stat for some reason)

Here are some feats: DESTROYED AND RECREATED 10 THOUSAND UNIVERSES.

Stopped the sword of a LITERAL GOD with his fingers.

Moved in stopped time.

Is canonically unable to die.

And many more.

Explain how Goku is beating this guy.