The ZETA HML has been proven to be a strong DPS performer in global, especially at P5T5. Transcendent is new to this unit, and without having T5, you are missing out on 25% accuracy, 36% beam damage, more importantly a constant 50% EX gauge recovery (not just the 1st EX) , and 200,000 damage cap increase (for future proofing). T5 makes a massive difference to this unit.
Put it this way, testing a friend's P5P5 Zeta HML, it is outperforming my P5T5 S Gundam against RED Coop II Raid (which S Gundam have a colour advantage on). In terms of ramping up, it does a better job than my P1T5 Sisquiede (with heaps of enhancement). Zeta HML is definitely a unit with excellent potential. The only disadvantage is that you can't fragment farm since it is not a limited/super unit.