Did it bother anyone else that the red/blue blocks in "Super Mario World" were empty?

This is probably the only thing that I don't really like about "Super Mario World" - the yellow and green blocks gave you Super Mushrooms and Magic Capes, so it would make sense to have something for the red and blue blocks as well - obviously, the red block would contain a Fire Flower, and the blue block somehow seems fitting for an Invincibility Star.
However, both of those blocks are empty, and I always thought that this was a shame.
Some people might say that this would have made the game too easy, but the Magic Cape is already kind of broken, especially when you have unlocked the Green Switch Palace and have green blocks everywhere.
And besides, the main reason why these coloured blocks seem so overpowered is because there are so many of them.
I would have preferred if all blocks had an item, and were harder to find.
Maybe Nintendo intended to have items in all blocks, but didn't have time to add this due to deadlines or something, or they might have simply forgotten about it.

It did indeed bother me, though it was never something I dwelt on for long.

I remember being initially disappointed that there wasn't something in them, but yeah, it wasn't a huge bummer.

It doesn't bother me too much either, but I do find myself thinking like "there should be a Fire Flower in that thing" when I see a red block, for example.
It certainly doesn't affect the overall gameplay experience, it just makes the game feel just very slightly incomplete when they are empty like that.

I have considered making some sort of modest hack where I basically just take the original game and fill those blocks with Fire Flowers and Stars, I think that would feel quite satisfying actually.

I don't recall ever noticing. I'm sure I have and it just didn't bother me. To me the switches were nothing more than additional platforms anyway.