You have dual boilers and claim that you can’t make a delicious brewed coffee with an immersion brewing method? That doesn’t exactly show a broad coffee horizon... *head shake*
By the way, I have a dual boiler and still like to drink brewed coffee.
I also have the dual boiler, as well as a Commandante C40, and I (also) really enjoy brewed coffee. But trying to teach others by claiming that making coffee in a tea infuser (!) has anything to do with immersion brewing makes me shake my head just as much. Well, this is also a house building forum, so no big deal.
Just as a note: what the pressure in your single-/dual-boiler or dual boiler ensures with a well-polished puck, namely an even contact of water with the grounds to enable a clean extraction, is done in immersion brewing by stirring (French Press or AeroPress) or the targeted, circular pouring. Maybe I’m just lacking imagination, but I don’t see how hanging a coffee-filled tea infuser into hot water is supposed to work. It doesn’t really make much sense either when you consider that tea in a tea infuser is supposed to steep, not brew. I could swear coffee is brewed, sometimes even cold brewed, but that’s just a side note.
Otherwise, I agree that good coffee doesn’t necessarily need an espresso machine, but it certainly doesn’t hurt to have one to make equally good coffee. Fundamentally, it’s very encouraging that people think about this, instead of just serving hot, black swill with tons of sugar and milk, but rather a delicious drink with a very diverse and wide range. But pretending that a TM is the jack-of-all-trades and has anything in common with a coffee grinder really goes too far. As already said, when it comes to coffee, the fun stops. No, it can’t make coffee, it’s not designed for that. And by the way, not for mixing concrete either, in case that’s going to be the next thing mentioned. Although that might be more likely.
Regarding the bean: yes, it plays a major role, no question, but not as presented here. Without a good grinder, you waste the potential of the best bean — or even more extreme: the best bean won’t help you if the grind size is wrong — and this is where it gets tight for the TM. There’s a reason very good grinders cost 0.5 to 1 times more than a TM. And that a TM would have a good grinding(!) mechanism would be news to me... it would certainly have spread in specialized coffee forums by now. So please, tone it down a bit. Do you need expensive equipment for passable coffee? No, definitely not. A good (!) hand grinder (approx. 50-200€) and for example a French Press or AeroPress (approx. 20€) and good beans are enough for noticeably better coffee than you get in 90% of restaurants, inns, hotels, and unfortunately so-called espresso bars. For French Press, the TM grind setting might even just about suffice in a pinch. But for espresso, that’s where the grind size limit is — and for the tea infuser anyway in every respect.
And a note on the chemist argument: just because I know how to hold a brush doesn’t make me an artist.
Making good coffee (like food) has less to do with mastering technical/scientific knowledge, and much more to do with artistry (as opposed to the overly intellectual scientist/engineer). It’s about enjoyment, sensuality, improvisation, creativity, and not about formulas, precise measurements, or some “correct” ratios between whatever. And especially as a coffee addict, you should know that every bean (of any age), every water hardness, every machine, every grinder, every ground coffee (i.e. quantity and grind size), and above all every person has their own individual recipe. You should definitely know the five M’s and their meaning. Otherwise it could get very thin, and thin coffee is rarely full-bodied and simply tastes less than something substantial with depth.