Just want to add: forma are for when you’ve run out of capacity after you’ve installed a reactor/catalyst. You can install them before, but it’s really inefficient.
Also, if you put all the basic mods on a weapon, and it still feels weak, take a look at its base (unmodded) crit and status chance stats. If, say, base crit chance is significantly lower than base status chance, then replace crit mods with more status/status chance, and see if that feels better. Same principle for frames: some frames have really low base shield, or their abilities don’t need range, or they don’t need to worry about energy management, so you’re better off swapping out some mods for others.
I use a lot of off-meta melee (if there is such a thing, since most melee can be made powerful). I guess the ones on my list that count as “mediocre” are Mios, Ninkondi, Prisma Dual Cleavers, Guandao Prime, and Twin Basolk. If we’re counting hidden gems, I’d also add Caustacyst, which I liked even before I had a riven for it, and now use on my Kullervo loadout as well.