Q: "Does Fireball allow a saving throw if a creature caught in it is chained to the floor by an ankle? Wouldn't it be more difficult to avoid?"Everything written in the game is interpreted BY YOU in how it's meant to be used. And telling someone else they are wrong makes absolutely zero sense.
A: "Yes, it does by RAW. Although if you wanted to house rule that there's some penalty for being partially restrained, you could do that."
For SOME rules questions there are simple and clear answers in the text. "Do Paladins get proficiency with heavy armor?" "Do Elves have Darkvision?" "Does Dimension Door have a Somatic component?"
Of course, questions with answers this simple are generally not the subject of debate.