People do form weird perceptions, especially from short trips to places they don't know well, but your numbers are wrong.
137/152 are the number of days w/ precipitation, not sunny days. ie, Seattle has less rain, but more days of precipitation. This is typical comparing Seattle with many other cities: less rain total, but spread over more days.
Those more days are concentrated in winter, more so than in is typical in other parts of the country. If you look at the "hours of sunshine" stat over a whole year in your links, the typical seasonal change people complain about in the PNW is right there: Apr - Sep are similar, but Nov - Feb Seattle gets half as much hours of sun.
The concentration of gloomy drizzly days in winter is quite real.
Undetectable is the standard of care and is the definition for the treatment "working". Viral load is checked regularly after starting treatment. If it doesn't become undetectable quickly with first line meds, there may be compliance or resistance issues and treatment approach is changed. With current protocols the main reason for treatment failure is mental health/substance abuse interfering with adherence.
The studies on transmission are using sero-discordant couples who are not using condoms. The evidence/confidence has been building over time with multiple studies in which no transmissions were observed.
The HPTN 052 randomized study was halted early because the evidence so strongly favored the treatment arm. In the PARTNER observational study, no transmissions were observed in the study at all. The evidence is very strong.