I asked mongol historian jack
"the Khwarezmian Empire. The Khwarezmain realm was very strong on paper, but a bit of a giant with feet of clay. Most of that empire south of Khursan had only been taken since 1200, so there was no long built institutional structure to give it strength. The ruling dynasty was Turkic, as was their main armies by the time of the invasion. However, these armies were Qipchaqs employed directly by the Khwarezm-shah, rather than raised from local Persian/iranian populations. The Qipchaps mistreated the local peoples and often, when the going got tough, abandoned the Khwarezmians. State and army were inherently fragile, and there was no Khwarezmian identity to keep the empire together in case of emergency. Infamously, when the Mongols attacked, the Khwarezmian leadership struggled to land on a plan of defense. While we might argue which was the best plan, the defense they ultimately chose allowed the Mongols to overrun Transoxania, Khurasan and Khwarezm itself city by city, and exasperate all the inherent weaknesses of the Khwarezmian state. To top it off, the Khwarezm-shah himself, Ala al-Din Muhammad, was overconfident in his abilities, yet terrified of the Mongols, knew nothing about their capabilities and lacked the ability to find out. Cowardly and unorganized, he was the absolute worst person to go against Chinggis Khan, a master organizer and leader who gathered all he could learn about his foe. Not a contest of equals, but rather more of an expert combatant attacking an amateur who was flailing his arms madly"
by the time the turks showed the sassanid empire had recovered from a low point Kavad and Khosrow reforms really helped so much so that noted the turks with the exception of the final war never could beat the sassanids to get anything close to the mongols who have to cripple the sassanid empire