Shri Kaustubh Karandikar Ji,
I also agree with you and my professional colleague about service tax being exempted under Sr. No.22 of Notification No.25 / 2012 - ST.
Kindly make sure that reply to SCN carrying enough documentary evidences to substantiate the fact that all service-recipient/s were GTA.
Depending upon 'hiring agreement', one can also try and see if 'Right to use these trucks / tempos' were transferred from XYZ to service-recipient/s / GTA. And if yes, purely as an additional defense, one can argue that no services were provided by XYZ and hence, question of service tax does not arise.
This is purely a risk-mitigation suggestion, so as cover a scenario of lacuna/s (if any) in proving availability of exemption (as 'burden to prove availability of exemption lies with person claiming the same').
W.r.t. potential factual aspects of pointed by Shri Kasturi Sethi Ji in above post, even the legal position that 'burden to prove availability of exemption lies with person claiming the same' will be seriously tested in court in these type of one-sided / without prior investigation SCNs.
All above should be treated as strictly personal views of mine only and not a professional advice / suggestion.