How is your contention any different from the argument which says that God knew Pharaoh would be a tyrant and would never believe, yet he still sent Prophet Moses to him?
Wa'alaikumu'ssalam,
I think it is not difficult to understand. It was necessary he is sufficiently warned about his wrong ways and introduce Islam to him. As you are aware, Allah would not punish any community without sending messengers and sufficiently send warnings.
Allahs says “Go, both of you, to Pharaoh, for he has transgressed all bounds;
But speak to him a gentle word, haply he might take heed or fear”. 20:43 “Allah directed Moses:
'Go thou to Pharaoh; he has rebelled,' And say to him. 'Wouldst thou be purified? And I will guide thee to thy Lord so that thou mayest fear Him. So he showed him the great Sign, But he rejected him and disobeyed; Then he turned away from the Truth, devising schemes; And he gathered his people and proclaimed, Saying, 'I am your Lord, the Most High. So God seized him for the punishment of the Hereafter and the present world.”(79:17-25)
Various ways how Pharoah was warned are explained at many places in Quran;
“O pharaoh! I am a messenger from the Lord of the worlds” (7:104)
Moses said to Pharoah
“It has, indeed, been revealed to us that punishment shall come upon him who rejects the Message of God and turns away“(20:48).
“Pharaoh said, 'Who then is the Lord of you two, O Moses? Moses said, 'Our Lord is He Who gave unto everything its proper form and then guided it to its proper function” (20:50)...."My Lord neither errs nor forgets. It is He Who has made the earth for you a bed and has caused pathways for you to run through it; and Who sends down rain from the sky and thereby We bring forth various kinds of vegetation in pairs. (20:51-53).
“Then after them We sent Moses with Our signs to pharaoh and his chiefs, but they wrongfully rejected them: So see what was the end of those who made mischief.(7:103)
And We showed pharaoh all Our Signs, but he did reject and refuse.(20:56)
“We have sent to you, (O men!) a messenger, to be a witness concerning you, even as We sent a messenger to pharaoh.
But pharaoh disobeyed the messenger; so We seized him with a heavy Punishment.” (73:15-16)
Then after them sent We Moses and Aaron to pharaoh and his chiefs with Our Signs. But they were arrogant: they were a people in sin.(10:75)
Please note Quran is not even addressing Pharaoh as a Kafir at the initial stage before he was introduced to Islam and deliberately rejecting the truth. Initially he was addressed only as "people defiantly disobedient" (kanoo kauman faasiqoon) 28:32 and people "exceeded all bounds"(20:24)