Yes, the Wago connectors with levers are prohibitively expensive for general use, this is why they are only used for connecting light fixtures here (about the only likely situation where you'd want to splice solid and stranded wires in "household sizes"). While stranded wire is perfectly legal for fixed wiring, it isn't used for two reasons:
- it's bigger. Since the nominal cross-section of stranded wire is the sum of the strand cross sections, there's always some air spaces between the strands that makes the outer diameter bigger than that of solid wire the same nominal size, and it's enough to be an issue.
- connections. In "extended VDE land" ferrules are mandatory for conencting stranded wire to anything but explicitly listed Wago connectors (the one with the levers), and most devices with push-in terminals (i.e. 95% of what you can buy today) aren't listed for stranded wire at all, unless special ferrules with gas-tight crimps are used... thus, using stranded wire will drive installation cost through the roof. So stranded wire ist mostly a DIY special. When I encounter it and can't replace I usually crimp regular ferrules and pigtail using screw connectors only for this run.
Tinning wire ends has been banned by VDE eons ago, I think late 50s or early 60s. Prior to that it was frequently done and each and every burnt Schuko plug I've seen had tinned wire ends... tells a story I'd say.
