Comfortable mediocrity... I wonder what we mean by that.
And by the way, congratulations on not making the discussion "all about you." Thanks.
Let's begin the discussion about the comfortably mediocre grand trine with a concrete example. Let's look at the chart of Bobby Fischer, the world chess champion. This chart has a perfect Locomotive pattern, i.e., the entire chart is built around, structured on, a partile grand trine in Air. I equate Pattern of the Chart = Pattern of the Personality = Pattern of the Destiny. or "What you see is what you get."
We have 5 planets in Air, to bolster the already structurally prominent grand trine. Look at the orbs between Mars, Uranus and Neptune... although there is a slight incursion by Neptune into the Second Degree, both Mars and Uranus are partile by degree and minute, and Neptune is only distant by 5' of arc: a partile grand trine, and all of the planets are included in two arms of the formation with the third arm empty. Here is a chart without equal for the study of the grand trine as defining the pattern of the life.
We also notice that Mercury and Uranus are in a 3-degree applying square. But the square is unusual in that, instead of emphasizing the Mode of the planets as is the normal case, what is emphasized by this square is the Air Element...Gemini is in Aquarius, Uranus in Gemini. These two planets are in mutual disposition of the chart: Fischer's IQ was measured during his high school days at around 185. Air is symbolic of "intellect" or "living through mental constructs in one's mind." [I normally use the traditional 7 planets as sign lords, but here Saturn -- lord of Aquarius -- is weakly aspected when compared to Uranus and his conjunction to that planet is separating and continues moving away by progression, while Uranus is brought to prominence in many ways, in particular his participation in the partile grand trine...so I give Uranus dominion in Aquarius here.]
Air is characterized as the thinking type (Jungian terminology). It connects facts, is objective and detached. The emphasis is on abstract thought, theory and ideas. Consciousness is directed at the most logical approach to life problems. This type is typically capable of very quick adjustment to changing conditions. Sails are trimmed and a new tack taken with every change in the wind. The course toward the main goal is maintained through constant tactical zigzaging. There is apt to be great volatility, an exaggerated flexibility that carried to its extreme is an instability of character. Air is rational, and when over-emphasized (the case in Fischer's chart...his life is structured on the trine formation, there is preponderance by element, and the chart is mutually disposed by planets in Air) tends to be cold and unfeeling. The person is inclined to force life into a mold of rigid formulas, motives and concepts devoid of feeling. Feelings, for the person with an over-emphasis of Air, is a minefield. Thought is valued for and of itself; there is little concern for the practical value of the thoughts as applied to reality, with self-satisfaction or approval being gained by the beauty and elegance of the thought-structure itself. His thought world is his reality. Air must continually validate its own existence by challenging and testing its theories against life. It seeks a continual reassurance, often and of necessity at the expense of others. Air is adroit at dealing with meaning, significance and implication. There is an exceptionally quick and facile ability to see the relationships among things.
When a planetary formation, and even more the whole-chart, is composed of very tight-orbed connections, life tends toward a compulsive and narrow expression. The tight orbs leave little "wiggle-room". Here the grand trine defining the whole-chart pattern (the personality and life-path) is partile to within 5 minutes of arc.
A good resource for understanding the functions and importance of the Elements and Qualities in horoscopy is found in Karen Hamaker-Zondag's The Elements and Crosses as the Basis of the Horoscope.
The characterization of a grand trine as inducing a comfortable mediocrity is made questionable by Fischer's chart. There was nothing mediocre about the man as he confronted an opponent across a chess board. He was, however, totally at a loss in any normal relationship with other people.
When analyzing a grand trine, look for the planet that beholds a square to a planet outside the trine. The aspect can excite the trine and move it away from its comfortable stasis. In Fischer's chart, Mars is the predominant planet, the motivating force in the chart. He is the leading planet in the whole-chart Locomotive pattern, is partile conjunct the horizon, disposes Venus who is partile conjunct the MC, and is participant in the Fixed T-square focused on his mother, the Moon...while opposed to Pluto at the Ascendant. The Air trine tells us that Feelings are difficult for this man, and the Moon at the apex of the Fixed cross confirms and reemphasizes this. Fischer had the delightful temperament of a shark. He once said that the high point, for him, in a game of chess was the moment he realized that he had destroyed his opponent's ego...the 7th House (Mars conjunct the Dsc) symbolizes "competition at the highest levels." Mars opposes Pluto.
I know I haven't fully answered your questions, but I don't feel like writing a book tonight. Hope this helps.