Since Universe 6 lost their potara earrings, and the 2 warriors left are namekians, and it would seem they might eventually fuse considering Champa tells them "you know what you have to do, don't you?" and they say "leave it to us, Champa sama" "We will defeat Universe 7" which would be a very optimistic thought if they rely in their current power level only which is close to Piccoro or Gohan, if they eventually fuse, how much stronger could they become? is namekian fusion stronger than potara fusion?
Correct me if I am wrong, but considering Champa's actions, words and behaviour so far I am pretty sure that he was trying to tell them to not lose. Which could either indicate to destroying the enemies (which seems very unlikely) or waiting it out. I think he meant waiting it out since it was said in earlier episodes that if at the end of the time multiple universes have warriors left then the one with the most warriors would win. Considering their power level + max power level with any given form of boost they wouldn't come close to Kefla. Even if they used Potara earrings. This is because of the fact that they have a fixed power level due to not having saiyan blood. They can power up a little with a ki boost, but nothing close to super saiyan.
Champa is no fool. He sure as hell acts dumb and crazy but his decisions are spot on and based on the current situation. That's why he told Kale and Califa to attack instead of hiding when their power levels were raising in order to destroy Goku. Their initial strategy was to wait it out and hope to be the universe with the most numbers at the end of the tournament after Hit was fallen. But Potara happened which drove Goku to UI. The 2 Namekians will never even reach the power level of SSJ2 Goku when they fuse. With Potara they might be able to force Goku to use SSG, but they can't boost themself more and more like a saiyan, so they will stay at that level while Goku keeps evolving.
Champa knows this as well based on what he had seen. He can be pretty sly as well so he might want them to use nasty strategies in order to reduce the enemy numbers. But it is either this or waiting it out. He definitely didn't mean to tell them to fight as that would mean the loss of his universe due to Jiren and Goku still being alive. Even with depleted stamina Goku requires only a couple of taks in order to recover again to use UI. This is based on the time that passed in the tournament (not episodes) between the first and second UI. Champa knowing this as well would not tell his warriors to fight against such a threat.
Edit: I just noticed that I had never answered your question and was simply just explaining the situation. The answer is no. Namekian fusion isn't stronger than Potara. Based on Piccolo x Nail fusion with the power levels before and after we can conclude that this formula is fusion power = (A+B)*7(raw estimate). Potara earrings scale far bigger and are known as the strongest type of fusion. When Vegito was introduced in DBZ we could see that it was far stronger than SSJ3 Goku. SSJ3 in general has a rough multiplier of x400 (some sources say x1000) from the base form. Since we have to consider Vegeta as well in the fusion we can conclude that the actual multiplier is at least x100 with Potara earrings. I couldn't find any credible source to explain the multiplier but based on before and after scenes and known multiplier for SSJ states we can give a raw estimate. Anyway Potara is far stronger than a namekian fusion. The most reasonable formula that I found for it was baseform A x baseform B. Some others said that it draws out max potentional achieved by each user and multiplies that by 400. But these aren't official sources.
So all in short, no, Namekian fusion isn't stronger than Potara fusion.
With regard to the comparison between the Namekian Fusion and the Potara fusion, I recommend you have a look at my answer here All possible fusions/absorbtions and their multipliers . Where I have explained as to why the potara fusion is a lot superior than all other fusions. And also why the namekian fusion is possibly the weakest form of fusion out of all the ones we have seen on the show.