Easy: it's like the old joke about a frog trying to escape a well by climbing a ladder... 2 rungs up, 1 rung down.
Without Brexit taking those 30 jobs away, the UK would have gained net 50 jobs. A much, much better situation.
Similarly for GDP. Our economy is still growing, but we went from being
theguardian.com/politics/2018/…
Instead, it's a long, slow slog. And just wait until Brexit proper happens, and the ladder goes away! Sadly, we ain't seen nothing yet.