Hi Josh,
The Map Image Layer is comprised of multiple individual map service layers and does not support the query operation. Each layer that it contains supports it.
The Map Image Layer supports the Export Map operation, which has the Layer Definitions parameter and can be filtered this way.
We had 2 dashboard created, one with the Portal Dashboard and one with Tableau. The Tableau map had no issues displaying the data, as I would assume it creates an image on the server. And with the Portal Dashboard I could not provide a map that performs reasonably, because I am forced to use Feature Layers, which require many rounds to the server to bring the data that is contained within each tile. And I have to increase the maxRecordCountFactor to actually get all the data back. The Dashboard overwhelms the browser and it freezes.
And I get it, we shouldn't show that much data on a map.
I just have to find a solution. And the Map Image Layer could be the solution if it works.