Both Switzerland and Australia are part of trading blocs.
If we don't need a withdrawal deal, what do you suggest happens in Ireland or with citizens' rights. Of course those issues need to be dealt with. We need a deal!
If there is no deal, the EU won't negotiate any trading agreements with us, especially if we don't pay our "divorce bill". We'll be stuck on WTO tariffs forever and be at the mercy of vulture economies, such as the US and China.
I can't think of any other major country which doesn't have some deal with its nearest neighbours, who have been up to now our biggest trading partners.
Yes, we most definitely do need a deal and we then need to negotiate tariffs, etc.