You are not wrong, but missing essential context. The American electoral system more or less ensures there can never be more than 2 competitive parties in any given election.

In some cases where republicans are not competitive, voting third party may be a reasonable strategy, but this is usually only the case in local races in very partisan districts.

If you want multiparty democracy (which I agree would be an improvement), it’s far more important to advocate for electoral reforms that would allow such a thing than to actually vote for third parties. To do so actually gives up your influence and can be an act of self-sabotage, even if your goal is to support third parties.