How do you know the Holy Spirit approved our rejection of Arianism, but not ...of infant baptism?
I don't really think this is the place to get into discussion of these issues, because we are all agreed on the christology which rejects Arianism, and we all agree that scripture teaches the christology of the ancient creeds. We all draw those conclusions from scripture; if, in addition, you have extra parts of Holy Tradition which confirm our shared christology, that matters not in re this discussion, for we all believe that the scriptures are sufficient anyway on this.
Nor do I think it is the place to get back into a discussion of infant baptism, for we have exchanged and explored our varied beliefs on that theme on one or more other threads at no small length.
However, since you are asking, not about why we believe in believers' baptism, but about how we reckon the Holy Spirit feels about infant baptism (if I am not writing all too anthropomorphically here), then let me repeat, as a purely personal observation, what I have written purely personally before: that I am fully aware that most of the great Christians whom Evangelicals admire have been pæobaptists, and - as far as Britain is concerned - a high proportion of recent and present great preachers whom God has used widely and powerfully have likewise been pædobaptist; indeed, some of the very best preachers - in terms of the blessing vouchsafed on their ministry - have been and are Anglicans. Therefore I have said, or will say now, that I believe we, as human followers of the Lamb, must do our best to fulfil his commands properly, and for us that means practising only believers' baptism. We do not have liberty to set aside right doctrine (orthodoxy!) and right practice, simply because God is pleased to use people more widely than our own beliefs. What God does is his prerogative, and infant baptism does not appear to have been a barrier to his powerful and gracious working. We leave that matter entirely and trustingly with him: he is, after all, God, or as C S Lewis says, "not a tame
Lion". But we must not copy the practices of anyone and everyone whom he blesses, but rather obey him as strictly and closely as we can.