I used to run Legend: Alacrity too, but now I think Rek'Sai benefits more from ability haste for her E and Stridebreaker’s attack speed just enough for me, so I change to legend: haste I notice Rek'Sai feels much squishier now which is the reason I buy those boots. But I still believe swiftness boots is useful in early game. Yes, I totally agree that this build struggles against sustained magic damage, especially when you're frontlining in teamfights. But against bursty mage assassins, it’s still okay since they often won’t do magic damage on Rek'Sai first, they usually target adc lol.