I would support this if: enough reasons were presented as to why would a mage select that partner he wants and a reason as to why that partner would accept their invitation.
Then, there is the problem that, in a mage vs mage scenario, the elite mages even if they are partnered with weaker ones are bound to give their team the upper hand, just because of their level. In a 2v2 situation, its a lot harder for the weaker couple to win when faced with an overwhelmingly strong opponent even if the weaker team showed top-notch cooperation. However, in a 5v5 situation, cooperation between multiple teammates can potentially overcome one very strong opponent.