it sounds like there's the possibility to shift the balance of 5 seats - however don't CA and a few other blue states have explicit rules against gerrymandering that preclude a tit for tat response?

So, am I understanding this correctly?

TX has D's at 12/38s with proposed changes bringing D's to 7/38s (ie 31% to 18% D)

And in retaliation, CA wants R's to go down from 9/52's to 4/52's (ie 17% to 8% R)?

BTW, IL has R's at 3/17s (ie 18% R).

But, somehow, TX changing the D's percent to match CA's and IL's R percent is somehow beyond the pale?

All states gerrymander. Both major parties do, too. The problem is the system of laws and practices that allow them to do it.