This opinion is rejected as directed by material passions (as described at the end of this post.). The "linear version" of Mesilat Yesharim summarized it in one statement:
שתכלית בריאת האדם הוא למצבו בעולם הזה.
that the purpose of creation of man is its situation in this world.
This is the main opposition between the Ramchal's opinion and this opinion.
This philosophy recognizes no other reality than being in "this" world. This is perhaps an allusion to Tsadok and Baytos, see Rambam on Pirke Avot (1, 3):
There were two pupils of Antignos, Tsadok and Baytos. They misunderstood the statement "אַל תִּהְיוּ כַעֲבָדִים הַמְשַׁמְּשִׁין אֶת הָרַב עַל מְנָת לְקַבֵּל פְּרָס, אֶלָּא הֱווּ כַעֲבָדִים {הַמְשַׁמְּשִׁין אֶת הָרַב שֶׁלֹּא עַל מְנָת לְקַבֵּל פְּרָס," and concluded both that there is no Sachar and Onesh.
The source is in Avot Derabbi Natan chapter 5 mishna 2:
אנטיגנוס איש סוכו היו לו שני תלמידים שהיו שונין בדבריו, והיו שונים לתלמידים, ותלמידים לתלמידיהם. עמדו ודקדקו אחריהן, ואמרו: מה ראו אבותינו לומר דבר זה, אפשר שיעשה פועל מלאכה כל היום ולא יטול שכרו ערבית, אלא, אילו היו יודעין אבותינו שיש עולם אחר, ויש תחיית המתים, לא היו אומרים כך. עמדו ופירשו מן התורה, ונפרצו מהם שתי פרצות: צדוקין וביתוסין. צדוקים על שום צדוק, ביתוסין על שום ביתוס. והיו משתמשין בכלי כסף וכלי זהב כל ימיהם, שלא היתה דעתן גסה עליהם. אלא צדוקים אומרים, מסורת הוא ביד פרושים שהן מצערין עצמן בעולם הזה, ובעולם הבא אין להם כלום:
Tsdukim say: The Pharisean tradition is to bruise themselves in this world and in the coming word they have no reward.
It's true that the approach of Tsdukim is more extremist. But their whole philosophy was a consequence of one premise only.
The first hypothesis in Sadducee's theory was the lack of future world. It's true that later this assumption took them deeper into heresy.
They found that their new philosophy may be congruent to Scriptures (they do not believe in Scriptures but know that politically, to say that they are agreed by scripture was better.)
The Ramchal intends to demonstrate a cascade of consequences of this premise:
The Mitsvot are for social and general well being in this world.
Ramchal presents conclusive evidences that Chachamim are against this premise.
Perhaps one per thousand would achieve the better use from this world.
The great complexity and details of mitsvot are useless if the intent is only well being in this world.
The human soul is at a very high spiritual level, and it is useless in this world.
It is possible to argue that this reasoning has an inevitable consequence for both, for the supporters of the premise and for opponents.
Supporters follow this reasoning up to its logical conclusion. There are no Judge and no Judgment, as Tsadock and Baytos concluded.
Opponents refuted the premise and concluded that the goal of man is his situation in the future world.
In his introduction to the discussion, Ramchal started with an analysis of the motivation of supporters of the premise, in the dialog version he wrote:
אין זה אלא טעות ותרמית הלב הנפתה אחר התאווה. ועליהם אני קורא: אם ללצים הורא יליץ.
It's only mistake and a ploy of the heart, which is attracted by desire. The following verse suits them well: "If it concerneth the scorners, He scorneth them". {cunning people are fooled by their own desire}
So the issue here is the starting point of the Sadducees reasoning.
Afterwards I want to add that the opinion of Ramchal is controversial. The Taam Etso disagrees and thinks that the man was created to honor Hashem. See this link.
Afterwards again, i found in the Peri Haarets a passage saying that the goal of creation is for the situation in Olam Haze,
וידוע הוא שעיקר בריאת העולם היה עבור עולם הגשם הזה החומרי אע"פ שהוא גוף קשה אעפ"כ יהיה מלא כה"כ ולכן כל הצמצומים והגבורות היו ג"כ עבור התגלות אלהותו ית' בשפלים התחתונים
I am almost sure that this is the point of the Taam Etso. So, we can say that the goal of the creation has a goal different from the goal of the man, from his subjective point of view. The man has as goal to discover the Creator the best possible. But the Kavod of Hashem is the effort made by men in this world. So, finally, I think that Ramchal is fighting Saduceans, not the point afforded by Taam Etso. I would be happy to discuss this with someone who knows Chasidut about this topic.