Chaos Marine defeating Halo Spartans image - Warhammer 40K Fan Group

you forgot the spartan laser which is pretty much a should mounted lascannon.

I must say, this is a fact. If you look at it, Spartans are from the time of the 3rd Millenium, thus quite early in human development (if we would count them as canon part of wh40k, which they thankfuly aint :P )
So compare these early human soldiers to a Space Marine. Even worse, a Chaos Space Marine, who has better equipment (archeotech by itself i better than new one, plus it is warp empowered).
So, look at what the thunder warriors did to the geneticaly modified humans during the Unification. It would take a company of CSM to wipe all of the Spartans (at max numbers) out of existance.... and propably every being in the Halo universe :P

Indeed Halo tech is quite primitive to current 40k.
Space Marines are closer to proper cyborgs than Spartans are due to the black carapace.

Thunder Warriors are more powerful than an Astartes individually and an Elite Guardsmen has better weapons than a Spartan(Hellguns,Plasma, melta .etc) does so neither comparison holds up.

Never seen a Forerunner or Flood eh? It's fine, I forgive you. Few people from 40k ever poke themselves out of the WAAAGH hole and view the other universes.

Pretty sure the elite,stronger,faster,smarter guard are called kasrkin however liking the idea of them being (These astartes aint good enough add more mansauce!).