My two cents on a couple things:
First of all, you say the performance adjustment is minor. My experience (over an absurd number of games recording the SR gain/loss on almost every single one of them, so I have a very good feel for “expected” gain/loss per game) is that the adjustment is very significant, and can very easily make up the difference between 15 points and 30.
Here are some stats to back this up, after entering all of my season 9 games (nearly 600 games) into a spreadsheet. Unfortunately I was tracking them all on post-it-notes by my computer, and after entering season 9 have exactly zero desire to go back to previous seasons, but I’ve started entering each match directly into the spreadsheet rather than on post its (while wondering why I didn’t just do that it the first damn place).
Games 585
Wins 302 52% 22
Losses 279 48% -23
Draws 4
Hog 153
W 75 49% 20
L 77 50% -25
D 1
Soldier 298
W 148 50% 21
L 150 50% -24
D 0
Moira 191
W 96 50% 25
L 93 49% -22
D 2
Winston 33
W 14 42% 22
L 19 58% -23
D 0
Mercy 34
W 11 32% 22
L 21 62% -24
D 2
The last number on the w/l rows is the average gain/loss per game.
The interesting bits here are that Moira is by far my best hero, that I consistently get the best stats with, Soldier is my “main” (the one that I want to play the most often) but that I know I don’t do as well on, and I just picked up Hog during the last part of the season, so obviously I’m not as practiced with him. Even if the difference was only between 20 and 25 points, that is still a 25% bonus/penalty, which is quite significant.
Second of all: I started recording stats because I was convinced that there is something seriously screwy with SR gains and losses, where I was consistently losing far more points for losing than I was gaining for winning. That is, in general, absolutely 100% true, and it is extremely frustrating. The overall difference between gaining 22 per win and losing 23 per loss might not seem that significant, but over 585 games that is over a full ranking level!
Here’s what I do know: that discrepancy is not because of the stats adjustments. I track stats pretty consistently on masteroverwatch, and here’s where some of the key stats lie percentage-wise:
Soldier
Elims: 1.96/min (top 65%)
Damage: 1149/min (top 71%)
K/D: 2.58 (top 47%)
Accuracy: 31% (top 75%)
Roadhog
Elims: 1.62/min (top 74%)
Damage: 1152/min (top 59%)
K/D: 2.59 (top 56%)
Enemies Hooked: 1.03/min (top 92%)
Moira
Elims: 2.27/min (top 41%)
Damage: 650/min (top 33%)
K/D: 3.76 (top 21%)
Healing: 739/min (top 86%)
Mercy
Healing: 1041/min (top 48%)
Ressurects: .7/min (top 14%)
Winston
Elims: 1.89/min (top 69%)
Damage: 711/min (top 62%)
K/D: 1.94 (top 75%)
Blocked: 929/min (top 75%)
With the exception of Moira healing and Hog hooks, my stats are all in the top 50-70% range. But my SR is low to mid silver, which on masteroverwatch is about top 90%, so my stats are generally going to be higher than others at my SR.
Which means that there is some other factor that unbalances gains and losses even more than what is shown here. I don’t know what that factor is, but it really pisses me off sometimes and frustrates the hell out of me. There is absolutely no good reason for Blizzard not to show the factors involved in SR changes.