This is a job for a charity - you're never getting stock + bonuses + competitive pay in a third sector job. UK pay is not near US but this is probably still median SWE pay outside tech roles and London + FAANG + others will pay closer with what you're suggesting with the mentioned bonuses/stock.
You are explaining why the pay is what it is.
I am comparing average pay in UK/US for a senior solutions architect position.
I dont understand what your comment has to do with my comparison of pay. Mind you, the comment I replied to speculated about this comparison. Hence why I provided more specifics.