If your lawyer states that the delay is a “substantial breach of contract” then on the face of it you should be allowed to cancel and deposit returned. However there can be many excuses why the build has overrun and when it finally comes to court it will be up to the judge to decide.
50/50 chance. You have to decide if the risk is worth it…no-one can decide for you.
As for sea view. Unfortunately no-one has automatic right to a view of any kind . What view you have today could be gone tomorrow.
Swimming pool. Why hasn’t your lawyer picked up on this issue? . I suggest you read your contract and the promotion material for developers are notorious for printing disclaimers which go unnoticed when buying and are never pointed out to purchasers.
You admit to being “more than happy” with the finish of the apartment so developers reasoning would be you have broken the contract not them.
Hopefully one of the lawyers will tell you my reply is incorrect and your deposit returned with hassle.