This, to be honest, is way Overpowered. Since, any and everybody could potentially craft end portal frames. If this is a Minecraft challenge (Minecraft but), then it's alright. But, if this is just a regular recipe addition pack, I'd say that you make the block a bit more expensive.

Just a suggestion, though. The final decision is yours. :)

I don't want to be THAT guy but:

1) simple low-effort data packs are against the rules
2) you should add a custom item that makes you able to break the end portal frame since they are unbreakable, and misplacing one would mean that it's stuck there forever and you can't remove it, you could use this to grief others
3) make the recipe end stone instead so you first need to go to the end before being able to craft it, do this by just replacing "minecraft:sand" with "minecraft:end_stone" in the recipe json file