There is no grammatical argument necessary as a plain reading of the text and its context suffices.Oy. You still aren't understanding. A "plain reading" *IS* a grammatical reading. A "plain reading" of the verse that violates grammar is a contradiction. It's a square circle. It's a married bachelor.
Context can clarify the unclear. It can't completely reverse the "plain text" grammatical reading of a clear verse. This isn't like John 1:1 where the true meaning of the Greek is highly debated, and probably will be forever. These verse are universally rendered.
1) Jeremiah 25:11 - It's seventy years of servitude for a plural number of nations. You appeal to context to change many nations into a singular nation. You appeal to context to change servitude into desolation (without an inhabitant) and captivity during the same time span.
2) Jeremiah 25:12 - There is an order of events, and the language used is clear 'When the 70 years ends, Babylon is punished'. You appeal to context to change the meaning to the exact opposite, mainly 'Three years after Babylon is punished, the 70 years ended.
In short - if you think you are conducting a "plain reading" without considering grammar, you are reading it incorrectly. You are reading INTO the verse.