i think the question ((esp. in v.6)) isn't 'did God make a mistake' - as in, did He choose the wrong people, but 'did God fail' - as in, was He unable to bring about the blessing and the inheritance He promised to Abraham.
what you're bringing up is reminding me of this:
. . do not look at the stubbornness of this people or at their wickedness or their sin, otherwise the land from which You brought us may say, “Because the LORD was not able to bring them into the land which He had promised them and because He hated them He has brought them out to slay them in the wilderness."
(Deuteronomy 9:27-28)
Moses's petition wasn't about Egypt perceiving that God should have chosen some 'better' people, but about the perception that God lacked power or authority to carry out His will, or goodness to follow through with what He proclaimed. similarly Moses said to the people:
“Know, then, it is not because of your righteousness that the LORD your God is giving you this good land to possess, for you are a stubborn people."
(Deuteronomy 9:6)
it ain't about Israel being a particularly great group of dudes ((not by works but by Him who calls))
Moses is pretty scathing in destroying any thought among the Israelites that they were chosen for their inherent qualities:
“Do not say in your heart when the LORD your God has driven them out before you, ‘Because of my righteousness the LORD has brought me in to possess this land,’ but it is because of the wickedness of these nations that the LORD is dispossessing them before you. It is not for your righteousness or for the uprightness of your heart that you are going to possess their land, but it is because of the wickedness of these nations that the LORD your God is driving them out before you, in order to confirm the oath which the LORD swore to your fathers, to Abraham, Isaac and Jacob."
(Deuteronomy 9:4-5)
"in order to confirm the oath which the LORD swore" -- see?
so i think it's more a perceived question about whether God is able to do what He purposed, than it is about whether God is wise to have chosen this nation.