I feel your pain, but to be fair to Squarespace, they have given you a solid answer. You cannot add any extra elements to a gallery page. You can recreate the effect by creating a new simple page and adding first a text block, and second a gallery block.

So what happens if they don't look identical? Well you have to learn CSS.

Overall I don't think that's an unfair conclusion to your question. The consumer platform on Squarespace is designed for non-coders and you can achieve more with it than you can, arguably, with any other non-coder friendly platform.

That's how I see it at least.