Moving from an A plan to a B plan isn't necessarily concessionary. It depends on the details.
An A plan has a cash value, including the risk, and a B fund has a cash value, including the risk. These can be calculated and compared.
As FBH points out, your individual situation may be very different in terms of time accrued towards the current A fund plan vs. time available to build value in some hypothetical improved B fund. Your taste for being personally responsible for the investment risk of a B fund vs. the company being responsible may be different than the next person's.
Don't write it off in some knee-jerk reaction. Let's see the details with some objective and clear analysis.