Depends on how many good cards you have. At season start, it's more difficult to get wins. 50% winrate is fine, if your average gametime is lower then 4-5min.
In my opinion any deck you are able to get 30 wins under 5hours is quite good. As I already wrote somewhere else, its bether to have a 50% winrate deck with a 3-4min average gametime then a 100% winrate deck with 10min average gametime.