After appointing and remunerating a judge, it would not be pragmatic for party to seek entire impartiality. In the eyes of the parties, it can be a simple boss - employer relationship where employees are expected to exercise what they are asked to do. Thereby, assuming the goal of the party is to win, arbitrator, as an employee will be asked to achieve this goal.
Then as was stated above, arbitration might become a matter of convincing the presiding arbitrator. However, the number of cases where arbitrators were challenged point out that parties do not have the same concern as I do