I feel it’s pretty flexible. If you needed to add another column, you would simply just need to add another piece, like & IF(E2:E = TRUE, E1 & ", ", "") and that could be reduced by removing the ‘= TRUE’ as it should still check against true. Like this & IF(E2:E, E1 & ", ", ""). But if you got something that works for you, go for it.
As for the second row… Some people like to join the column heading and formula in the first row (see @Robert_Petitto’s example) . I like putting my formulas in their own row. I do it in the second row without data because if the formula is in a data row and that row is ever deleted, then you lose your formula as well. My way isolates the formula from any data. As long as you structure the array formula with an If statement, (where I check for length of a particular column) then Glide will not see the second row as it appears empty.
I tend to freeze my top 2 rows for my own reasons, but I think there is a little known feature that might work for you. Freeze your top 2 rows for your header and intermediate formula and Glide will ignore any visible data in the second row. I have not really tried that myself, but it sounds like an option that might work.