: If you really have 10 people simultaneously recharging with only 1 attacker, and you cannot hold on to a portal for a very long time, then your side is doing something wrong. Keep in mind too that eventually the shields will all be destroyed, so you are no longer at max mitigation.
Assuming the portal is down to the final R8, it still takes three uncontested X8s to destroy it, maybe two if the attacker gets a critical hit. An X8 will inflict about 2000 XM per hit. Ten people recharging will dump 10000 XM into the resonator. The recharging will easily keep up with the damage. The attackers also have ten times the inventory, and each Q8 (8000 XM) is worth over three times an X8 (2000 XM).
If you are unable to defend under those situations, the problem is not with the portal. It's with the players.