As a certified rap head from the golden age of hip hop (mid 80s through late 90s), I somewhat agree. But I will admit that while I used to be a hard liner on that like you, there has indeed been some good underground rap music of the last 15-20 years. It's hard to find and I guess it depends on what you like out of your rap music, but there's some good stuff out there.
In regards to Biggie, Live After death was incredible. But personally, I thought Ready To Die was every bit as good and it of course came first. It set the stage for that new wave of rap music. If you're not familiar with that album, you should be.
Tupac - meh, he never really did it for me. By and large, I'm more of an East Coaster than a West Coaster but I respect Pac. I just never got into his music all that much. I loved him with Digital Underground though.