This user's frustration is entirely justified, and the real problem isn't Excel's behavior, it's that the tool gives you no way to say "yes" to row expansion but "no" to column expansion for a specific table. That should be a simple toggle, but it isn't. And when a workaround exists, like inserting a hidden column, the fact that users have to resort to it reveals a gap between how spreadsheets work and how people actually work.
Here is the practical reality: when you place a spill array in the column directly adjacent to a table, Excel treats that spill as a column extension. The table absorbs it, and you lose control. The user's desire to keep row auto-expansion while blocking column auto-expansion is not an exotic request. It is a natural consequence of wanting to use dynamic arrays, one of the most genuinely useful additions to modern Excel, without sacrificing the structural integrity of a table. The hidden-column trick works, but it is a bandage. You should not have to hide data or add invisible scaffolding just to keep a table from eating your formula.
Our opinion is plain: Microsoft should give users per-table control over auto-expansion behavior. The current all-or-nothing approach forces a false choice. You can disable auto-expansion globally, but then you lose the row-expansion convenience that makes tables valuable. Or you accept that every spill array will stretch your table's column range, which breaks layouts and creates cleanup work. Neither option respects the user's intent.
What this means for you: if you are building a table that needs to grow downward but must stay fixed on its right edge, you are stuck with workarounds. The hidden-column method is the most reliable, but it adds a layer of friction that should not exist. For now, treat it as a pattern worth adopting: insert a blank column between your table and your spill array, set its width to zero, and move on. It is not elegant, but it is effective. And if you find yourself wishing for a per-table property that says "expand rows only," you are not alone. That is the feature this use case demands.