Fr. Longenecker is engaged in building a strawman here, based on the dread word, "modernist." (Whatever that means....)
I seriously doubt that Fr. Longenecker is truly unable to find even a single "modernist theologian" who is able to believe in a "God who is both immanent and transcendent." It sounds like wonderful reason to leave ... but I suspect that the good Father is telling a lie.
Don't get me wrong: there's plenty wrong with what passes for theology in the Anglican churches (on both the "revisionist" and "orthodox" sides, it must be noted). But to simply condemn Anglicanism on the basis of an ill-defined epithet is not helpful; and it's not honest, either.
Over the past few years I've had the unpleasant opportunity to see at close hand the sorts of arguments that are unleashed by clergy engaged in self-justification. Fr. Longenecker's screed positively reeks with it.
For a good, complete definition, you may wish to read Pope Pius X's encyclical letter, Pascendi Dominici Gregis. Written back in 1907, it really forecasts a lot that has happened within the Church.