No.
Here's why.
The UK can control it's currency and maintain a clear direction. The EU can't do that. The Euro favors some countries.
The UK can have bi-lateral trade deals that is best for her with all countries around the world[1]. The EU can't do that, it has to consider ALL countries best interests within the Block.
The UK can change it's business rates to be more competitive than the EU [2]. The EU can't really do that, lest it risk some states losing money.
In short. The UK is in an excellent position for growth.
[1]: https://www.theguardian.com/business/2017/feb/07/uk-g7-econo...
[2]: http://www.telegraph.co.uk/news/2016/11/21/theresa-may-to-of...
I'm actually rather bullish about the UK. Remember, when the UK had trade deals with countries around the world? We'll have that time again.
[1] https://fullfact.org/media/uploads/Trade%20deficit%20and%20s...
[2] https://econsnapshot.files.wordpress.com/2014/11/gdp-us-eu17...