Same setting as Avengers: Infinity War, except Namor and his army decide to assist the Wakandans, as Thanos' snap will affect them just the same.
Namar + an equal number of Talokan to the Wakandan warriors we saw on the battlefield. They have their standard vibranium spears, axes, clubs, hydrobombs and each has a air-breather.
Thor and crew show up at the same point in time as well.
I think the problem is that there didn't seem to be that many Talocans.
Each individual Talocan seemed more formidable than the average Wakandan warrior and the higher-end Talocans like Attuma looked to be at least on par with supersoldiers if not more, so they'll definitely be able to demolish quite a number of Thanos' forces.
Namor on his own could possibly be the strongest force in the battle prior to Thor arriving.
The problem is I don't think there's enough Talocans to really turn the tide of the battle. And unlike Thor, Namor doesn't have quite the same AOEs to take out swaths of enemies.
The Talocans sucked. Wakanda should have steamrolled them but instead got nerfed into the ground in order to make Namor's people a threat. They previously had fleets of ships (instead of like the three we see in the latest film), energy projectile weapons (which were stated in the first BP film as capable of oneshotting a tank), energy shields etc. which they apparently forgot about here for the most part. And their army was tiny. I wouldn't be surprised if there were less than 200 onscreen during the biggest battle. And their ships, which could go toe-to-toe with Thanos' forces during the battle in Endgame, were being damaged by roided up water balloons. It was fuking stupid. Namor was formidable but, realistically, a platoon of regular soldiers armed with conventional weapons would have wiped out his entire force without issues.
__________________ Never take life seriously. Nobody gets out alive anyway.
Namor said he had more warriors than Wakanda had blades of grass, but who knows how exaggerated that was.
Why I made the stips be that he'd bring an equal number of his warriors to match the Wakandan number on the battlefield, which consisted of the different tribes.