If the boss is using their own personal advisor they have likely drank the kool aid and there is not much you can suggest. They likely trust their financial advisor over you, and don't see anything wrong with the fees, even when presented with evidence. I went through the same thing with my boss, and when I presented evidence it was rebutted with "paying 1% in fees is completely reasonable to have someone manage your investments". I can relay all the information I read from MMM, and JL Collins, and the various financial books I've read, and show him a chart of compound interest with an extra 1% taken out, but his mind was made up and he liked the advisor and believed the advisor had his best interest in mind and would earn his 1%.
That said, 0.4% is not that terrible on the spectrum of all possibilities. It's not optimal, and much higher than you'll pay in your own IRA, but it's also outside of your control so you just have to deal with it. Hopefully the funds themselves have a low ER and it's not egregious. Even when it is it's still probably in your best interest to utilize the tax advantaged space. You probably won't be employed at this place forever, so you'll be able to roll your balance over to your own IRA at some point and eliminate those fees at that point.
