It's not just segwit, it's the number of transactions that has gone down
Actually right now we're below January 2017 levels, far before the spam attack

The good news is that it will be expensive for the spammers to flood the network. Let's dare them to do it again to show the whole community that Bitcoin's blocks can reach 2mb because Segwit.
Let's just ...not!
Bitmain could just unplug their miners for a few hours and the whole capacity gained by segwit will be destroyed by higher blocks time. I just hope that they still have two brain cells active and don't try to put such plan into action.
3. with SegWit we got about 20% capacity increase (so far) which helped a lot and also some of the big services started batching their transactions which improved things a lot too.
This is actually one of the main reasons for the drop in transactions and it was clear when Coinbase went offline for a few hours.