i understand and agree that the baptism which is effectual is not the one done by human hands but by the hand of God. this, Simon Peter also understood at Cornelius' house, when he saw that the Spirit was poured out on unbaptized Gentiles the moment they believed -- but that apostle found it ludicrous to withhold water when he saw what God had done.
Paul also understood this when he wrote explaining that the circumcision which is effectual is likewise not the one by the hands of men, but the cutting of the heart by the hand of God. God also understands this, yet He commanded Abraham, and He commanded all the Israelites in the law, to do this in the flesh.
i agree that in our day, H2O immersion can be just as much a hypocrite's idol and a snare as circumcision was when Paul wrote Galatians. i think, however, that in terms of this thread topic, our time is better served in establishing that the keeping of this sign when it is not of faith may be as damning as taking the cup of communion "in an unworthy manner" -- as sending a message by the hand of a fool ((Prov. 26:6)). i do not believe you have a case for the claim that H2O immersion was not practiced by the disciples or the early church:
(1) it seems clear to me that Acts 10 is a definite counterexample
(2) there is abundant historical evidence of its early practice in terms of a continuation of those things passed down by the apostles
(3) just because you don't see the word "water" in Paul's epistles doesn't mean he did not teach it -- his epistles when they mention baptism are expository, speaking of the meaning of the signs, meant to instruct in wisdom, and he makes distinction between 'immersion' and being filled with the Spirit. a clear example is 1 Cor. 1:14 -- he himself baptized some -- compared with later in the same epistle, 1 Cor. 12:11-14, where he indicates that all of us are baptized by the Spirit - the Spirit's own work. throughout the NT the disciples laid hands on people in prayer, that they might receive the Spirit - a different action than baptism.
i see Acts 10 as an insurmountable hurdle for your argument -- not for the argument that H2O immersion by the hands of men is neither strictly necessary nor sufficient unto salvation, but for the argument you made that the apostles & the church never practiced it after pentecost.