But where is it written that it must be one or the other with no in-between. Certainly one advantage of the 401(k) system is its portability. I know of many state workers for whom the pension is a set of golden handcuffs; the closer they are to retirement, the less able they are to move on to other opportunities.
A better option would be to provide a fixed amount of retirement benefit, which the worker could then choose to direct a part to a DBP, and a part to a DCP. The sponsor would invest the DBP portion, and guarantee its return (the risk for which could be outsourced), and the worker can invest the DCP portion.