I had originally done quite a bit of tinkering with tectonics for my world’s map, but found I wasn’t getting the results I was looking for/getting frustrated with just how much was involved to feasibly replicate it.

I found my fantasy solution: while the world was still molten hot from its creation, great elder beasts were plopped down on it, and in their ensuing melee, the mountains, hills, oceans, and trenches were formed. Their now dead forms can still be found on the world, many of the largest mountain ranges, island chains, and deep sea trenches found along their breadth.

I didn’t really answer your question, but you had me thinking of bashing my head against my keyboard for a couple of weeks some time ago!