I think Keyman doesn’t impose the typing order on people. Whether to type the letters before the tone marks or to do the other way round is entirely up to the keyboard author. For example, on the keyboard I work on, which is now in Keyman repository, you type the letters before the tone marks, just the way you would write in a book.
It’s also optional to use dead keys. So on this keyboard I work on, there’s no dead key on the desktop layout. However, there is one dead key on the android layout, but I’ve already removed it in the new version. Once that is released, there will be no dead key anywhere in the keyboard. I feel people should immediately see the effect of what they are doing; and typing should be as normal as writing by hand, but faster.