Nice theory, but the reality of how these decisions get made is usually far less interesting. Some product owner probably wanted the iMessage enabled texter to

Nice theory, but the reality of how these decisions get made is usually far less interesting. Some product owner probably wanted the iMessage enabled texter to "pop" and the designers usually take that and roll with it usually through some combination of boldening one, and deemphasizing the other to give the overall desired effect. It's a good call out for them to improve the color contrast, but you can adjust the contrast yourself through the accessibility options.