To be honest DFW-TPE only really hurts EVA themselves most, as they interline heavily with Alaska on that route to SEA.

Delta's very weak to DFW and only has one flight that connect to SEA-TPE that has an uncompetitive 7am departure + 6am layover. Delta flies two daily A220-100s between DFW and SEA, which is a testament to their weakness on that route.

I imagine EVA has assessed the market and expects sufficient interline and local yields out of DFW to make it work. 3x weekly isn't even that much anyways.