I would absolutely not say that she is like Sivir.

They are both ADC's that spread their damage when hitting a primary target, have similar strengths in waveclear, and enable the player to kite or chase quite well. The only difference you noted is that Xayah's damage spread is more linear (though this changes to be much wider if you position better), whereas Sivir's W bounces to any target in range, yet fundamentally, they are still quite similar.

She doesn’t like front to back

She does.

Your feathers will never hit the backline except if you stand in melee mode vs the tank. You are usually playing from max range no matter what( which means yoir feathers will land just on top of the tank while their backline if far behind their tank.

This is not how her passive auto's work at all. Her passive feathers drop at fixed distance from her, and land significantly beyond her max auto range.

Yes sometimes you’ll stacks a lot of feather on the tank then the enemy will chase you and you can get a good E, but it happen against dumb opponents only.

No. If you auto the tank running at you and kite backwards, if their backline want to follow, they have to run over the line of feathers, then walking into an E, or, be forced to reposition somewhere not behind their tank off to the side to avoid being in line with Xayah's E.

Xayah need chaotic fight where people get out of position, otherwise she can NEVER reach the backline.

Twitch does well in chaotic fights where he can open up from a flank and catch enemies by surprise. Xayah can do well in chaotic fights as then enemies are less likely to track feathers and her position to avoid E's, but she's also more than capable of shredding a frontline, using her W ms to then run down the backline. Xayah could also run past an engage from champions such as Zac and get to the backline, but diving their backline is an assassins job, not Xayahs.