Interesting question, although I think it is based on two false assumptions.
Premise A) Hashem created the world in order to bestow ultimate goodness to those that adhere to the correct path.
Premise B) Whatever the correct answer to the question of free will, ultimately Hashem still foresees the future.
Thus being that He wants to only bestow good, (A), and he ‘knows’ that this person would under his own free will not be a recipient of it, on the contrary, he will be punished, (B). Why did he create them?
On the face of it, premise A needs clarification on multiple levels of analysts. The phrase תכלית הטוב להטיב, is given as a cause for the creation of the world, i.e. the ultimate ‘goal’ of a supremely good being is to bestow goodness onto others, thus He must create the world for that end. However it doesn’t explain why we need to ‘work’ for this good, why couldn’t Hashem just give us the ultimate reward without the hardships need to acquire it? That is why we say נהמא דכסופא, i.e. by definition a complete reward is only one that we worked for and deserve it. This in a nutshell is the rationale behind the Ramchals opening remarks.
However, on the face of it, if we think into this it would seem that the reasoning is flawed. First of all, why do we need to say that Hashem is the ‘ultimate good’? Presumably because if he wasn’t, then it would take away from his Omnipotence (שלימות). But doesn’t saying that since he IS the ultimate good, and that means bestowing onto others ‘goodness’, that in itself takes away for His שלימות? Think about this way, if he would NOT have created the world, He would not have unto whom to bestow ‘goodness’ thus He would be missing in שלימות, as תכלית הטוב להטיב, that would then mean that His שלימות is DEPENDENT on others, c”v.
Furthermore, this would imply that insofar that the world was not in existence, (i.e before בריאת העולם), and there was no one to ‘favor’ then he was at least at that time, missing in שלימות c”v.
Another point would be that we know that Hashem is פשוט בתכלית הפשיטות, how can we attribute to him middos and wants? Only humans are capable of such things because we can change, not Hashem.
If this is incorrect, and his שלימות is not dependent on actual bestowal of ‘goodness’, (thus His שלימות is NOT dependent on others), then why did He need to create the world at all? (Which was the reason of stating תכלית הטוב in the first place).
Thus we can safely assume that we are lacking in understanding what תכלית הטובל להטיב means.
As to the premise B). The general understanding is correct. The question of free will is not asked as such: since we have free will, how can Hashem know the future, rather it is always (to my knowledge) phrased like this: since Hashem knows all that is going to happen how can WE have free will. In other words the question is on OUR free will, not on HASHEMS’ divine knowledge.
The difference of phrasing imply that whatever the answer, what is constant is Hashems knowledge of the future, whereas if it would have been phrased the first way, that would imply that Hashems divine knowledge might not be constant. Obviously the reason for stating it the second way is because Hashem must know the future for if not it would be taking away from his שלימות, (and another reason which is tied into this one).
Now we can answer the OP question. The concept of תכלית הטוב cannot mean in regards to the initial reason of creation, as explained above, rather it refers to the moment in time when the attribute (Sefirah) of Chesed was created. Then we can say that whatever is created through the Sefira of Chesed (which in this case is the world in general) was created in such a way as to be able to give full and complete Chesed to its inhabitants. However we are not referring about Hashem proper c”v, since He Himself does not have any attributes whatsoever.
But, in regards to free will, that is not talking about the level of the sefirah of Chesed, rather of a higher dimension, one without time. Thus the question why did he create wicked people knowing full well that He would not be able to bestow goodness to them, is incorrect, since the ‘knowing’ and the ‘wanting to bestow’ are two different dimensions.