That makes me wonder about your computer in terms of memory and processor. I really cannot say I have had any of those problems you report. I have playlist with hundreds of songs and while I notice it slows a bit the more you add, it still works very well.
In regards to missing artist I would assume that has to do with licensing agreements for Canada. Here in the US, there are even a few artist missing, but I do not blame Slacker for that. You take Bob Segar for example, he is just a moron! His music isn't on Amazon or iTunes. He is a control freak and some artist are like that.
In most cases I have created my own stations for most of the genres I wish to hear. I have had a blast doing that and sat radio cannot touch my self created Slacker stations. Overall there are a few pre-programmed Slacker stations which have very good playlist.
I do not see Slacker as a replacement for Sat Radio either, though clearly some do and have canceled their subs. However, when I want to here what I want instead of some voice tracked dj that plays a lot of crap I do not, then Slacker is the clear winner. You cannot ban artist or songs on Sirius XM. You get what they deliver and most of the time that is okay, but not all the time.
The point is there will always be folks that complain about software and sevices. Does not mean everyone feels that way or even have those problems. Using a forum as a means to prove your point that Slacker creates nothing but buggy software is nonsense. It would be like showing someone the SL2 forum and then saying see, that is what you can expect from Sirius XM. That would not be a true picture because we know on the XM side we have gotten updates for our hardware and software.