Rapid has different possibilities, not less, no more. Just because we now have a more expansive arp or multiloop mode, it doesn't mean that it will be practical for bread'n'butter sound design and overall usability. Drums? Why would anyone, beside presets makers who cater to people who want to play split sequences, program their drums in avenger when you can't even have more patterns triggered by different keys?
In 1.7 Parawave has even overhauled the whole look of Rapid, provided a much better theme alongside a different font (much more readable, and it proves that taller narrow fonts don't necessarily make a more readable text, especially if that font scaling and aliasing is very bad), which, by Manuel's words, is not going to happen in Avenger. Beside that, a good environment affects the way you work and, just like physical tools, if you're more comfortable using something you'll just work better. Anyone who ever tried rapid can confirm that it feels much smoother and snappier. It fits in a laptop display (which is good, on the contrary of what someone thinks, people also work on laptops sometimes).
You see, there are a lot of pros and cons for both, but unless you consider specific aspects there is no "better" one, just different possibilities.
And if you think in other terms, there is much less to point out about Rapid then there is about Avenger. And as if that's not enough, some criticism might even pass as personal attacks if you aren't too careful with words.