We have to understand various factors about this verse, some of these factors are linguistical (ancient Hebrew), others are logical. But, all of them are to be understood inside the whole-Bible context.
First of all, the words used in Genesis 48:22 (Masoretic Texts) cannot refer to the purchase of the piece of ground at Shechem (Gen 33:19).
In fact, Keil&Delitzsch’s Commentary on the Old Testament explain why: “[...] for a purchase could not possibly be called a conquest by sword and bow; and still less to the crime committed by the sons of Jacob against the inhabitants of Shechem, when they plundered the town (Gen 34:25), for Jacob could not possibly have attributed to himself a deed for which he had pronounced a curse upon Simeon and Levi (Gen 49:6-7), not to mention the fact, that the plundering of Shechem was not followed in this instance by the possession of the city, but by the removal of Jacob from the neighbourhood.”
So, having cleared this point (by logic) we have to linger over – briefly - the God’s process of ‘nomenclature’ (in the meaning of ‘giving a name’ [linked to a character’s traits, or linked with future deeds a person will do in the future]). Some of more famous examples of this God’s method was the names He gave to ‘Abram’ and ‘Sarai’, changing these names, along with their meanings, with some new names which did reflect better the new circumstances this two Bible characters lived.
The pivotal point is that Jacob’s name – too – was changed by God.
In fact, when he was about 97 years old, and after the struggle he did with the ‘man’ he did meet, God said (through the angel): “Thy name should be called no more ‘Jacob’ but ‘Israel’: for as a prince hast thou power with God and with men, and hast prevailed” (KJV).
As we well know, this name was applied to the entire nation coming from his 12 sons.
The last point is linked with linguistics. I believe this short space is not the apt place to speak thoroughly about the linguistic peculiarities of ancient Hebrew language. In synthesis – for a lot of people this would be a shocking statement – the Masoretic Texts (from which we predominantly draw our OT translations) offer us no linguistic hints about the temporal factor to insert into the verba forms. In other words, all the temporal conjugations of us – to the past tenses, present tenses, or future tenses, are inserted in an OT translation only by context. They are added – on the basis of the context – to complete the sense of Bible wording.
To conclude, we may say that the patriarch Jacob (Israel) in this verse embodied himself the en-tire nation of Israel, expressing – through God’s inspiration – some prophetic glances about this nation.
John Gill (Exposition of the Entire Bible) rightly asserted: “[...] Jacob, under a spirit of prophecy, foreseeing and declaring that his sons, and he in his sons in future time, would take it out of the hands of the Amorites, the principal of the Canaanitish nations [...]. [...] by giving to Joseph this portion above his brethren, it appears that the birthright was become his [Joseph], he having the double portion [...].” (the same concept we find in the Keil&Delitzsch’s text abovementioned)
So, a better translation of this verse in question would be:
“And I [Israel] will give to you [Joseph] a shoulder [or, ‘an allotment of land’] more than to your brothers, which I [Israel] will take from the hand [or, ‘the control’] of the Amorites with my sword and my bow.”