Certamen – the method in Ars magica that two wizards decide an argument over an issue – makes about as much sense as two skilled swordsmen strongly disagreeing about who owns some spoils of battle, and deciding to play cards to see who is better (ahem)..at playing cards. In setting characters who are gamblers might decide to play cards to decide, however that is very character dependant.
Essentially Certamen is a magical contest which is favours the powerful wizards. Higher art scores and basic skills will defeat many opponents.
It might be legitimate as a tool to use in a story, but does it make sense in the setting’s wider themes and context, and is it plausible? I’m doubting that it does.
If I disagree with another person and I know they are “more powerful” or stand a much better chance of winning, that does not invalidate the discussion or issue at hand. Saying that a wizard would defer their logic and rights to a magical competition does not make sense, especially so if they are not likely to win. Even in contract negotiations where one side has basically all the leverage (say a buyer in an over supplied commodities market) there are negotiating tricks and player to be found.
Basically the stakes of the issue need to be low enough that the result of a Certamen will be honored by the magi who looses, and high enough to bother with a formal duel. Which is to say not very often. Certamen comes back to character ego, a sporting activity, and a strange game mechanic, not a method for resolving disputes. Sure, edge cases are available, however I don’t see Certamen regularly used in games and certainly don’t see characters prioritizing their advancement to account for it.
So what’s the solution? Well that depends on what the players want from Certamen. The current model does use a range of skills which has a higher skill point cost, but conversely it is difficult to be great at everything. The current mechanics have done well.