I think she's one of the worst SRs. I'd rather SR++ Sandra twice than use a Riza.
I guess my stance comes from my emphasis on Mega Bosses (PVP is worthless right now IMO). When you are fighting a mega boss with high defense (i.e. anything relevant) just about everything but skills does zero damage. That means high skill damage wins. Even if it only goes off 1/4 of the time that skill will be one of the only relevant attacks in the cycle.
Lets look at a really good R card and compare it to a bad SR card.
Sharo (R) has a max skill damage of 10k. Rebecca (SR) has max skill damage of 8400. Dreadnaughts/Neos have 6500/7000 defense. Rebecca may use her ability somewhat more often, but it will do almost nothing, and Sharo also has a massive edge in crit. In short, Sharo is preferable to Rebecca on Mega Bosses. Granted, most SRs are better than Rebecca, and most Rs aren't quite on par with Sharo. Still, just because a card is a higher tier doesn't instantly make it superior.
Charisma cost does matter because getting 3x SR++ requires like 140 charisma. That much CHA comes at the expense of having lower stamina/focus.
By good cards I'm assuming you mean SRs. (If not, then I agree with you.) At level 60 with 5 weeks played, I have 2 SR++. One of them is single-leveled (so not amazing). The other is 3x leveled. All other SRs I only have 1, or I haven't seen drop at all. That's with maxed active comrades and assisting on every mega boss that I can. Naturally, over a long enough period, yes, I'll get a ton of every card. However, I think most of us will have quit this game by this time next year so what we can obtain within a month or so is what's relevant to ease of acquisition.