An excellent point.
All Trinitarian baptisms are valid. That is why Protestant baptisms are recognized by the Church.
Sects that have rejected Trinitarian theology (JWs, Oneness Pentecostals, Christadelphians) and sects with heretical Trinitarian theology (Mormons) do not perform valid baptisms.
Baptism is the manner by which we join the Body of Christ. Sans valid baptism, an individual is not Christian.