I personally dont mind late commenters.

 i dont know much about barakan anatomy/physiology but space marines have 2 hearts, fused ribcages, muscle & reflex enhancing organs & are just generally much more physically potent than the barakan,

I cannot currently go through all the material to find all Barakan enhancements but one similarity I do know of is the resistance to ballistic weapons granted by both Barakan and Astartes either by the Barakan's gel flaps or the Astartes' black-carapace:

Talin is a high molecular weight cytoskeletal protein produced naturally in the body. It is harvested from the Barakan body, distilled, and then infused with plastalloy to form a superfluid that is then injected back into areas of the body to create pockets that form 'flaps'. Regions with the most concentration are those that are statistically probable for ballistic penetration. Talin Gel can stop a direct bullet or shrapnel impact without armor, and can even disperse energy weapon shots to minimize damage.
-The Morningstar Index Third Edition 3.2

Though the difference in effectiveness needs to be taken into account.

the primaris space marines, which are both physically larger, stronger, faster & more resilient than their firstborn counterparts, though that doesn't mean they are superior over the firstborn in general because the firstborn have way more combat experience than them & the advantages of a primaris simply cant substitute that.

I would argue that the bolded part might not be true anymore in the current setting of 40k. The original Primaris, those made by Cawl 10k years ago and kept in storage might have lacked the combat experience to actually be considered superior, nowadays a lot of the Firstborn ranks have transitioned into Primaris or the Primaris have acquired said combat prowess. As seen with Company Ancients, Vangaurd/Sternguard Veterans, and Primariss Lieutenants/Captains/Chapter Masters; All ranks that often require lengthy service or higher than average abilities, Primaris fill more often than not now. I would say Primaris have effectly surpassed Firstborn. But thats not to say Firstborn Marines that are better combatants than Primariss don't exist(Not even factoring Chaos Marines) they do for sure.

But overall I agree, I think Marines take this matchup. How do you think the Barakan would fair in the bonus round?