One thing I'd say is that it's not always the techniques that feel the hardest that actually offer the most benefits. I believe Buddha's term "middle way" referred to a way that was in the middle between extreme privation/altered consciousness and the ordinary world. I think those interested in meditation techniques should consider this.
And in terms of long term silent retreats, I had an old friend who's schizophrenic symptoms were intensified by retreats of that sort and meditation in general isn't a thing that's riskless - I recall the possibility of serious reactions to meditation and intensive meditation in particular has been documented in a number of articles.
Which relates to claims about "All problems"
I wouldn't describe a weeklong meditation retreat as the "extreme" side of the Buddha's middle way. That would be more like starving yourself in asceticism. With the right practice/preparation (IE a few months of daily hour-long sits), I think a weeklong retreat would be beneficial and reasonable for most people.
Of course, getting to the point of a daily practice is pretty challenging itself, but not too much more than the average workout routine in my opinion.
In Qi Dao, our approach is based not on going beyond a person's comfort zone but extending their comfort zone.
Maybe it’s a difference of perspective, but what you describe as practice already sounds pretty extreme to me.
A very very corny way I like to think about this is the separation of the init process (being) from other processes (thought, sensation etc.). I know this is a very superficial interpretation, but I find it helpful.
This is key. Too much importance to thinking and thoughts otherwise all around. See even during "meditation" we tend to talk about "watching thoughts" like they are something special worth that attention.
I went to a 10 day silent meditation retreat (Vipasana) abs felt I got much more comfortable sitting by myself just observing my thoughts. The practice part was difficult, probably one of the hardest things I have ever done. 10 days of no talking/reading/writing, sitting in a room, observing your sensations, for hours on end, punctuated by 5 minute breaks. I felt the world temporarily go from HD to 4K after a couple of days.
Anyways, this really made me reconsider my relationship with thoughts. I feel I can separate the sense of my being from my thoughts some times. This helps me with my anxiety.