"As we move more and more into a world in which employees ... are the ones responsible for their retirements, and in many instances for much of the cost and even management of their health benefits, the competency of plan operations becomes more and more central to our, as well as courts', thinking about ERISA plans, responsibilities, and liabilities. This is becoming an explicit and literal concern ... with legal doctrines governing ERISA litigation moving towards a framework in which problems with competence can more readily be remedied through the court system."