Brexiters claim we send more money to the EU than we get back.

That's only true if we assign a value of zero to all the benefits of EU membership.

eg trade deals: they don't directly bring the UK Government cash, but they underpin trade supporting millions of jobs. Worthless?

I covered this in more detail in a long thread a little while back. It's still as valid today as it was then... https://twitter.com/uk_domain_names/status/1230404441926402049

Brexiter logic would suggest that a gym membership or Netflix subscription must be worthless because they don't return as much money as they cost.

Thing is, the issue is about value not about cash: you subscribe to Netflix because access is worth more than the subscription fee.