I briefly tried a Welsh for Adults course, and fell into all of the traps you describe so beautifully!

However I’ve been pretty successful at learning Welsh with a self-designed and self-motivated combination of simple online resources. (SSIW podcasts, Memrise, BliuBliu, later audiobooks / Radio Cymru). These fit in around the rest of life rather than taking up specific time for themselves.

Massive implications for formal learning, but no bright ideas what to do about it!