Among the people already inclined to believe him and the idea that this is plausible, it won't do any damage to his credibility. Among the rest of the population, which is conditioned to see any accusation that the CIA is involved in some sort of conspiracy as evidence that this person is a crackpot, yes, it's going to be a big limiting factor on how his wider message is viewed. If your goal is to spread a message that goes against the mainstream narrative, the last thing you do is give them ammunition to paint you as a crackpot.
Your prescription for messaging is not without merit. But context is key.
Sometimes, however, and arguably at this time, the hammer blow of a direct, devastating public indictment of the kind that Malone has so manfully leveled is necessary.
Malone has certainly not made the mistake of bringing a knife to a gunfight.
His allegations may enable Trump to patch things up with his supporters disappointed with his unabashed pro-vexxationation stance and “messaging”. I say this based on the following premise: First, the allegations are eventually proven true and
Second, (as is likely to be the case) Trump was totally unaware that the so-called “Intelligence Communities” of the U.S. and the U.K. could be and eventually would be used in this way, to indirectly attack their own peoples.
Trump could then point to the Donkey Party and say, See, my fellow Americans? Whatever it is they accuse Trump of doing, they themselves either have done, are doing, or will do, or, and as you can plainly see in this case, all three!