It's Netero who is said to have survived against Maha, not the opposite, and Zeno precised that Netero is the only of his opponents who fought him and survived. The Dons's best subordinates were the the Shadow Beasts, who had all been killed by the Troupe.
Oh, ya, that's true, it was that way arround.
I still don't think it implies who has won or even at which point in time it happened.
If we take into account that zeno freely admits he is weaker than netero even tho netero is much older let's me suspect that netero is in fact stronger than maha.
It's not Maha who is sent to the most dangerous missions, and even Zeno does a support job for Silva in their fight against Chrollo.
I think it is pretty clear that the guys the zoldyeks send if there is a really dangerous mission is the zeno-Silva tagteam.
Maha must have been very strong at some point when he clashed with netero, but i really don't think maha as he is now would be in the same league.
There even might be anice backstory hidden here: Maybe Netero was actually defeated by Maha and this was the reason for his insane training in hell (after all, he was already of some age when he did that training and not a youth anymore, so their clash has a good chance of having happened before that training).
To the shadow beasts: it is true that the shadow beasts were the nen team of the ten dons, but that didnt hinder them to hire at least some nenbased bodyguards in yorknew.
It is not a stetch to at least give it some probability that they had nen based bodyguards at their meeting.
I don't think the zoldyeks would want to lose a son due to being careless, so sending maha with them would make sense to me. It enable Kalluto to make some first hand experience while being perfectly safe.
It might also have been the zoldyeks wanting maha to evaluate kalluto's skills while illumi focusses on the job.
After all, at some point after this job, Kalluto joined the spiders. i don't think silva would have agreed to that if the zoldyeks didnt deem him ready.
All in all, i cannot see Maha being stronger than zeno or silva at this point, and at least zeno is not as strong as netero by his own account.