you raise a good point, in my understanding God is one who is perfect , devoid of any dependencies, even not dependent on its attributes; pure , prefect , truth ; there is verse in Quran

He is the First (nothing is before Him) and the Last (nothing is after Him), the Most High (nothing is above Him) and the Most Near (nothing is nearer than Him). And He is the All-Knower of every thing.

when we say God is 1 in 3 and 3 in 1 ; it raise multiple issue

if he is perfect than ; then why it needs a son/daughter; because now it depends on the wishes/decision/influence of them

when 1 take a decision; and other differs even .0001 percent to it ; then whose decision will be fulfilled, because than it is not Omnipotent

historically this concept of trinity is not taught by any prophet, then why does the nature of God suddenly change

if Adam/Eve did a mistake why I should inherit that, which make God unmerciful and unwise

Jesus died for our sin and our salvation becomes dependent on just believe on him, that this voided all the wisdom, capabilities, circumstances God has given to us ; since I can do what ever I want and can still attain heaven while a pious person will go to hell; this make good illogical and unwise

In short trinitarian God become a lesser/illogical/unwise/dependent god than God ; than is it really a god?