Around 10 years ago I had a Solitarie to my keychain. I then found this to be nice and pretty bright for it's size...
I cannot compare now, but have hard to believe that a Solitaire with fresh battery is dimmer than Quark AA2 on moonmode. The reason to that low brightness can be that the bulb to Solitaire (the same with Minimaglite bulb) after a while will be carbonised on inside and therefore lowers the output.
I didn't mean to put it down, but it is dim now, and I like its dimness.
I figured that its most likely due to an ancient bulb. I've had that light for almost 8-10 years, as well, and haven't replaced the bulb yet. Honestly, I love that its so dim, because it allows me to navigate around my house without harming my night vision at all, when getting up to get a drink or visit john.
I don't bother putting it on my keychain, because I EDC the AA^2 and my 6P with a LF 250-lumen P60 LED module in it. Between the two, I can see everything from a few feet away, to a few hundred feet away. Plus, I have 2 Lighthound LED keylights on my keychain, for when I don't want to use either of my good lights.