Get all columns in custom visual

I'm trying to build a custom pivot table visual for PowerBI, and to do that I'm using the "matrix" dataview mapping, like this:

"dataRoles": [
        {
            "name": "Category",
            "displayName": "Category",
            "displayNameKey": "Visual_Category",
            "kind": "Grouping"
        },
        {
            "name": "Column",
            "displayName": "Column",
            "displayNameKey": "Visual_Column",
            "kind": "Grouping"
        },
        {
            "name": "Measure",
            "displayName": "Measure",
            "displayNameKey": "Visual_Values",
            "kind": "Measure"
        }
    ],
    "dataViewMappings": [
        {
            "matrix": {
                "rows": {
                    "for": {
                        "in": "Category"
                    }
                },
                "columns": {
                    "for": {
                        "in": "Column"
                    }
                },
                "values": {
                    "select": [
                        {
                            "for": {
                                "in": "Measure"
                            }
                        }
                    ],
                    "dataReductionAlgorithm": {
                        "window": {
                            "count": 30000
                        }
                    }
                }
            }
        }
    ]

However, I'm having trouble with the API not returning all the data.

In particular, if I add a lot of columns, a warning appears on the visual saying that there are "too many values" and that not all of them can be displayed.

I've read about the "dataReductionAlgorithm" property, but setting it on the "columns" prevents the visual from loading at all.

I've also read about the "fetchMoreData" api, but invoking it doesn't seem to help at all with the problem.

So, is there a way to get all the columns in a matrix? Or am I just s**t out of luck and I have to get data in simple table format and pivot it myself in code?