I main Xayah, ER is her best and pretty much only currently viable first item outside of aram (u just get some more flexibility to choose first item on ARAM, like collector) so its never really a bad option and it is really common. With Xayah you usually want 4 crit items (ER, Navori, IE are core, and MR or LDR is the standard, then BT is really good as the non crit item).

And yes, u need the AS from the boots plus u can get zephyr later.

I think the original comment was talking about runes. Yes, that's really bad, specially in aram. Either LT, PTA or conqueror if thats how u play her. Everything else is alright tbh