Segwit conservatively frees up 60% of block size.

Let say each trans is 250 byte with 1MB block

60% X 1MB = 0.6MB X 1024 X 1024 = 629,146 byte

629,146/250 = 2,517 transactions

2,517/600 = 4 TPS

we get 4 transactions more per second....I don't think that should be called scalability!