1. why did you assume I meant 1.2.4?
2. OOA adds gameplay in the sense that you don't care about your health, you only care about the crystal. It also is one of the updates which added the most items (I think the third?). It is true in the sense that it is an add, but that makes it all the better. It brings that new feel to terraria, and vice versa. Also it's optional, adds a new currency, powerful weapons, many turrets and more.
3. Fishing isn't overpowered because with an obsidian skin potion it'll take you, what 10 min for pickaxe? It took me 2hrs to get reaver shark once I started fishing, which was after I had a deathbringer pickaxe. It'll take you as long if not longer to fish a full set of hardmode armor, and it will cost you bait, but in my opinion It's more exciting to fish (I don't have the patience to mine until I have pickaxe axe or luminite pickaxes) and in crimson worlds the ores can be quite rare.