I think you have two good options here. The first is for the whole engineering team to present a united front to the team lead in a meeting and make the case fo

I think you have two good options here. The first is for the whole engineering team to present a united front to the team lead in a meeting and make the case for what the technical approach should be moving forward so that the team can help ensure the success of the company (aka your livelihoods). The second is to tell the founder that the team lead needs to be moved out of an engineering lead role and either into product management or into a non-lead engineering role for the sake of the company (aka the founder's reputation).