I wanna stick up for Lavazza, but with the caveat that darker, robusta driven beans want a cooler temp.
I too have been driving myself nuts with an microcasa lately, it can be tricky. I've used a moderately hacked gaggia classic for several years with fine luck, and have on occasion returned to it out of frustration. The thing with all this stuff is that all the factors mentioned exist simultaneously, which is why folks often emphasize changing one thing a time. Generally, lighter coffees require a finer grind, preinfusion and warmer temps. Even if you dial in the lavazza perfectly, trying your same technique with a lightly roasted Ethiopian will not give a good cup. Similarly, folks telling you how long they warm up the machine is only a bit of temperature management, the set temp on the pstat, the routine- to flush or not to flush, a single cup vs several in a row, etc. all effect the cup greatly. I don't say this to get you down, but to say that it is hard, it's not just you.