I explained why I don't like Life Orb in my write-up of Tornadus-T in my original post. 10%(LO)+25%(SR)=35%. Regenerator regains 33% of my health. 35-33=2. A net 2% loss in health if I use LO and my opponents have rocks, thus negating Regenerator. Additionally, again in my write-up of Tornadus-T, the power drop from Life Orb to Sharp Beak is actually negligible. I don't actually lose out on a lot with Sharp Beak. The difference between Specs and Sharp Beak however, is huge.
The problem with SubSD Terakion is that it doesn't fit on my team. Terakion's purpose on my team is to revenge kill. Meanwhile, adding SubSD would force me to try alter my team to deal with the things that wall it, while I don't have to worry about that on Scarf Terakion since I am not trying to sweep their team with Terakion, I'm just trying to punch holes in things. Also I lose Stealth Rocks. That's actually a pretty big loss.
Also, the issue with running Lando-I is that it doesn't actually fit on my team. Lando-T has a super specific niche for this team, being a defensive pivot that still manages to hurt things. Combined with Amoonguss, I have two very deadly pivots that force switches and put my opponent into unfavorable positions.