The Actuarial Valuation is carried out by independent actuaries. I assume that the relative fund growths are dependent on the investment profile of the respective funds. That investment profile is also determined by legal constraints which vary with the makeup of the scheme members.
Roger Maynard is resigning because of his position with the pending Iberia merger. The BA pilot's elected trustee is very sorry to seem him go and feels his skill, knowledge and expertise will be difficult to replace. He also feels he could have remained. It is a mark of the man's integrity (now there is a quality we rarely see these days) that he is resigning at this point.