So then it depends not on human will or exertion, but on God, who has mercy.
Romans 9:16 ESV
That verse does not support you
It is not talking about unconditional election to salvation but the fact that God sets the grounds upon which he shows mercy
and this has not changed
Romans 3:21–26 (KJV 1900)
21 But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets; 22 Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference: 23 For all have sinned, and come short of the glory of God; 24 Being justified freely by his grace through the redemption that is in Christ Jesus: 25 Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God; 26 To declare, I say, at this time his righteousness: that he might be just, and the justifier of him which believeth in Jesus.
1 Corinthians 1:21 (KJV 1900)
21 For after that in the wisdom of God the world by wisdom knew not God, it pleased God by the foolishness of preaching to save them that believe.
or just try reading rom 9-11 in context
Romans 9:30–32 (KJV 1900)
30 What shall we say then? That the Gentiles, which followed not after righteousness, have attained to righteousness, even the righteousness which is of faith. 31 But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness. 32 Wherefore? Because they sought it not by faith, but as it were by the works of the law. For they stumbled at that stumblingstone;
Romans 11:19–23 (KJV 1900)
19 Thou wilt say then, The branches were broken off, that I might be graffed in. 20 Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear: 21 For if God spared not the natural branches, take heed lest he also spare not thee. 22 Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in his goodness: otherwise thou also shalt be cut off. 23 And they also, if they abide not still in unbelief, shall be graffed in: for God is able to graff them in again.
Those who came by way of faith found mercy the other did not