IMHO, the main value a tech cofounder should bring to an existing idea is the expertise to avoid tech as much as possible. Most ideas are not doing anything revolutionary technically and you can go very far just by cobbling together stuff from off the shelf tools. You need a strong technical vision to avoid the temptation of overbuilding and focus on just enough tech to support your current phase of validation and that’s a unique and valuable skill.

If you have a company that primarily relies on some novel technical accomplishment to be viable, it should be something founded by a technical co-founder IMHO.