imo

First off,
Boost leak test, and actuator test,

then start looking at wastegate and housing cracks/leaks


But on a RST 0.36 housing, it will need to be mega cracked to cause bad spool up issue's, i've tested a badlt cracked housing on my TT, and it was less than 100 rpm slower on spool up to hit 25psi then a new uncracked housing, on a back to back test.
New hit 25psi @ 2450rpm, cracked = 2500rpm.


Edited to read clearer, and more info.