There's a distinct lack of quality Heavyweight opponents full stop, more of them are in the UFC though, and the better fights will not come "on the circuit". Outside Alistair, Fedor and Werdum there's very, very little "on the circuit". Big Foot Silva's OK, but he wouldn't be anywhere near Top 5 in the UFC. My Top 10 HW's would be:
7 UFC fighters, 3 SF Fighters. That's effectively "the circuit" right there. The only guys outside that Top 10 worth considering are Struve, Big Foot Silva and Schaub. Arlovski's on a horrible run, Barnett is past his best days and can't get licensed in the US and after that there's very, very little. This so called "circuit" doesn't exist. There is no-one else outside the UFC and Strikeforce, and outside Fedor, Werdum and Silva there are no legitimate opponents left "on the circuit" for Alistair to fight. You don't need to be in the UFC to fight the best, but the large majority of the best fighters in the world are in the UFC, which happens to be why it's the best MMA organisation in the world. This isn't some massive ZUFFA Marketing ruse to fool fans into believing inferior fighters under the UFC banner are better than guys outside the organisation, as much as you'd like to believe that the case. Another thing worth considering is that Strikeforce can't get their HW's to fight, even less so than the UFC's. The reason the UFC HW's haven't fought many times is due to injuries, Strikeforce just have no control over their guys. Fedor feels the need to re-negotiate his contract every couple of weeks; Alistair disappeared to Japan for a couple of years, not defending his belt for almost 3 years; Barnett can't get licensed and they're running out of contenders so Big Foot had to fight a blown up LHW. This mystical "circuit" you constantly talk about doesn't actually exist.