Did the TK player bring his SSC? Did he bring a Casket?
The SSC is practically required these days due to the usefulness of its fire damage against certain very popular Regenerating creatures (like Hydras...). And with True Line of Sight, it'll be somewhat more difficult to avoid looking at the Casket (and iirc, the Hydra doesn't have a great leadership value...).
Also, it sounds as if you at least got lucky against the Ushabti. A quick mental tally of the numbers (though not a careful one) suggests to me that the Ushabti should have taken the Hydra down.
Aside from that, it's not really a surprise. Tomb Kings have problems with things like the Hydra. Nor, it should be added, are they a particularly good match-up for Witch Elves, which will chop them up into tiny itty-bitty bone chips (29 poisoned attacks, rerolling misses? Oh how did you know it was my birthday!?). You might want to try testing him out against a few other armies first before you decide to shelve him.