When people say 3/4* are viable, they usually mean you indeed promote them to 5* and merge them. Lon'qu in particular is pretty good with his prf.I wish someone had told me that 3/4* units could be viable before I spent so many feathers on a Lon'qu 😅 But yeah never really considered the possibilities of using 3/4* units as they are, and merging to get them as stacked as possible. Still it makes sense that 5* units aren't always worth the investment, especially in PvE, since they're expensive and getting multiples of them in the first place is incredibly inconsistent. The best I have is a +2 Nowi and though she's incredibly powerful, the thought of needing all those feathers and praying on gacha to even give me a spare Nowi, makes me grit my teeth a bit lol.
Regardless, I'll definitely give investing in a 3/4* unit(s) a shot. Is there a proper way to go about building one, or is it essentially the same as a 5*?
Now, 4*+10 heroes are pretty decent too (equivalent to 5*+5 iirc), but I like my golden borders.