Trailblaze doesn't provide Fire Resistance on activation, or at least not enough to nullify the fire damage you receive from it.
Trailblaze's weapon description states it provides fire resistance, however its entry in the Runic Grimore says it does not and in practice it does not.

Steps to reproduce:

1. Get a Runic weapon with Trailblaze on it
2. Hit a mob until Trailblaze triggers
3. Take fire damage for a few seconds
4. Oops! Well, you should probably reroll it if its "obviously broken", oh wait, that's a Runic Halberd... rip

Using the All of Fabric 6 modpack.

Thanks for the report.
Trailblaze's description now properly reflects the ability in the latest release for 1.19.2.
It is intentional that it causes self damage.