Should not have a cooldown due to the vast (1/6th MP) cost associated with it already, in addition to this the largest part of the damage of sword oath is just the auto attacks and with what I am suggesting the main tank would only use sword oath very briefly (1 or 2 auto attacks and a royal authority) before "weaving" out of it. If it was found to be too strong if anything it should just have a 1 or 2 second cd and be increased if it is found to be too strong from there, but I think leaving it as having no cooldown would make careless paladins prone to run out of MP anyway.