If that’s the case, no Protestant baptism would be valid. At least not any Evangelican baptisms. I don’t know of any Evangelical who believes Baptism is necessary for salvation.
They might… they might not; the more mainline Protestant denominations generally have a similar understanding of the necessity of Baptism as the Catholic Church, so it depends upon the intention of the one administering the Baptism. In High Church Anglicanism, Lutheranism and especially Anglo- Catholicism most if not all Baptisms are valid; however in these cases we cannot know, which is why when Protestants (of any denomination) converts they receive a conditional baptism (“If you are not yet baptised, I baptise you in the Name of the Father and of the Son and of the Holy Ghost/Spirit”). In fact the ONLY other Church we can be sure of having valid Sacraments is the Orthodox Churches (which is why we are allowed to receive them when lacking Catholic ones).
With Baptists we have none of these assurances, as there are three things needed for a Sacrament to be valid, matter, form and intent. If even one of these is lacking, there has been no sacrament conferred
Requirements for a valid Baptism
Matter- pure water
Form- the act of washing along with the proper Trinitarian formula
Intent- for the remission of sins, or at least “doing what the Church does”
The Baptism administered by the Baptist churches
Matter- pure water
Form- the act of washing, with the Trinitarian formula
Intent- a public expression of personal faith or obedience to God; aka the “Believer’s Baptism”. As they are an extreme Protestant sect they assuredly do not intend to do what the Church does.
Due to the lack of proper intent, there has been no baptism and the one being washed remains unbaptised. Baptists due not have valid baptisms.