reward punishment - Implications of "According to Your fear is Your anger" ("כיראתך עברתך")

It says in Tehillim 90 (a chapter attributed to Moshe Rabbeinu, if that affects anything):

יא: מִֽי־י֖וֹדֵעַ עֹ֥ז אַפֶּ֑ךָ וּ֜כְיִרְאָֽתְךָ֗ עֶבְרָתֶֽךָ: לִמְנ֣וֹת יָ֖מֵינוּ כֵּ֥ן הוֹדַ֑ע וְ֜נָבִ֗א לְבַ֣ב חָכְמָֽה: 11 Who knows the might of Your wrath, and according to Your fear is Your anger. 12 So teach the number of our days, so that we shall acquire a heart of wisdom.

I saw in another translation: "According to the fear of You is Your anger."

I was trying to find out what all this means and saw the following gemara (Taanit 8a or thereabout) :

אמר רבי יוחנן כל המצדיק את עצמו מלמטה

מצדיקין עליו הדין מלמעלה שנאמר אמת מארץ תצמח וצדק משמים נשקף רבי חייא בר אבין אמר רב הונא מהכא (תהלים צ, יא) וכיראתך עברתך

§ Rabbi Yoḥanan said: Whoever is exacting with himself, by striving to act righteously in every way on earth below, he is judged in an exact manner in Heaven above, in order to improve him further still, as it is stated: “Truth springs out of the earth, and righteousness has looked down from heaven” (Psalms 85:12). Rabbi Ḥiyya bar Avin said that Rav Huna said that this idea is derived from here: “And Your wrath is according to the fear that is due to You” (Psalms 90:11). The level of God’s wrath correlates with the offender’s fear of God.

ריש לקיש אמר מהכא (ישעיהו סד, ד) פגעת את שש ועושה צדק בדרכיך יזכרוך הן אתה קצפת ונחטא בהם עולם ונושע אמר ריב"ל כל השמח ביסורין שבאין עליו מביא ישועה לעולם שנאמר בהם עולם ונושע

Reish Lakish said that this principle is derived from here: “You took him away who joyfully performed righteousness, those who remembered You in Your ways, behold You were wroth, and we sinned, upon them have we stayed of old, that we might be saved” (Isaiah 64:4). This verse also teaches that God displays wrath specifically due to the transgressions of those who are accustomed to acting righteously.

This is all very difficult to swallow. It seems to say that one who sins only occasionally is punished more harshly for his sins than one who sins frequently. How does it not fly in the face of the entire reward and punishment doctrine? (Is it suggesting, for example, that one is still rewarded for increasing observance, but with diminishing returns?)

We have a mitzvah to fear G-d at all times, said Rambam or maybe Rashi. But the assertion that "the level of God’s wrath correlates with the offender’s fear of God" is hardly encouraging in this matter. (How can we give our utmost in this mitzvah anyway?)

Finally, how does this all square up with the known idea (again I can't find the source, but I am quite sure it exists in Chasidus Chabad if not elsewhere--I think it is the primary thought underlying the over-the-top efforts we make for Pesach, for example) that one endeavors to go beyond the letter of the Law precisely out of love and gratefulness to G-d for His own chesed in dealing with us? It seems quite backwards that we should set ourselves up to incur punishment if G-d forbid we fell short of our ambitions.