that quote can be interpreted in different ways.
you seem to be interpreting it as ‘so long as I don’t go too high for too long, everything is fine (and I get to eat treats regularly).’
I and others on this board interpret that quote as ‘the organ and nerve damage from blood glucose levels above 7mmol/l is longterm and cumulative, and may not become noticeable until a great deal of damage has already occurred, making future management increasingly difficult, and diabetic complications becoming more and more likely as time goes by.’
it is, of course, everyone’s personal choice as to how they evaluate their personal risk and how they manage their health and lifestyle.
my personal view is that I am 53 and would like to live another 30+ years in good health, with eyes, feet, hands and internal organs all functioning well. So I don’t want my blood glucose rising to damaging levels at any point during the day which will, over the years to come, cause cumulative damage. I also like to keep my blood glucose well below damaging levels at all times, to give me a nice safe buffer zone.
Because I am human, I don’t always achieve this, but I achieve it consistently, and when I err, I keep my blood glucose well below 11mmol/l
Your mileage may vary, but you mentioned ‘quality of life’.
I make decisions that will improve my health a great deal in future decades, which will in turn improve my quality of life.