OK, I think you may be right - though in practice there is often enough solder on the iron to make the joint anyway, and feeding more in would just add to the mess to clean up. I'm talking about small components here, or edge joins in 0.018 thou brass. With experience you can (usually) see whether the solder has wetted the brass, and if in doubt, a stress test usually finds out one way or the other.
BTW, the 1 cm^3 lump in your example is relatively massive compared with the thin brass etch stuff - I can't imagine soldering anything to that cube with my 50W TC iron, would probably use a gas burner.
Look forward to it.
I don't have an analysis, but these things usually have bismuth in them. It's a very good compromise: it wets brass far better than genuine low-melt solders (70 deg and 100 deg are readily available, the latter being a bit stronger) but doesn't require furious heating. With care, it can even be used on white metal if the latter is not too low in MP. It is marketed by Carr's in 0.5 kg reels, or by other model suppliers in smaller amounts at considerably higher unit cost... Let me know if you would like to try some.
Heavy engineering!
OK, didn't spot that.
I generally try to avoid using a conventional soldering technique on etched brass - solder cream, RSU or sweating are all preferred according to circumstances as they all leave less cleaning up to do. The conventional "run hot iron + solder along seam" approach is still useful for large butt joints, and you can usually do those from inside where it doesn't show. (Actually, experts still use an RSU for that, but I haven't quite got to that level of proficiency yet.)
David