I think that the question was more to if we take the scripture command to have only these allowed to partake of Lord's Supper, why not be consistent and apply the commands regarding who is to be water baptized?If I am understanding the question properly, then your “Reformed Baptist” is mixing up two positions that are different. The commands to repent and be baptised were directed in the preaching of the gospel to unbelieving adults.Whereas, (1Cor 11:27) is an instruction to the church in observing the ordinance of the Lord’s supper, and the necessity of examining themselves (v28) as to their spiritual state as Believers. So chalk and cheese.
It’s like saying that because the All blacks have beaten Wales so many times, then Wales should not play rugby! But we know we play it as it should be played.