You can easily rank but don't expect any top 30s.
The staff does not equal skill i have seen so many people with it do terrible even in almost bis gear so it is definitely possible to get a ranking parse
What will help ranking: Staff, Cunning of the Cruel, Dark Intent, Tricks of the Trade, Power Infusion, Focus Magic. Be sure to pre-pot and pot during bloodlust as well. Having shadow fiend out prelust is a good dps boost too.
With DI it is definitely possible. If you play 10mans the comp you are playing is much more important than having legendary. Also, the legendary was much more gamebreaking in tier 4.2 where it was impossible to rank better than 50+ unless you were solo aoeing on beth or Rhyolith. In tier 4.3 you can easily get ranked 30 or better without legendary if you have a 410 substitute and DI.
I didn't have legendary in start of 4.3 but I still managed to get ranked around 30-50 on Ragnaros heroic 25man and some DS encounters. After I got my legendary I did get top 1-5 rankings on every boss (either lfr/normal/heroic) though. If you didn't get a lot of rankings in tier 11 and start of tier 12 you probably shouldn't aim towards any current ones seeing as you probably aren't good enough and don't have the right mentality.
Originally Posted by lappee
last few posts state that the encounters are equally hard, but its just more difficult to get 25 good enough players
If you want to pull 'decent' ranks, then you'll need some supply of buffs.
Dark intent is nearly essential
Power infusion is MASSIVE
tricks of the trade can be really useful if you can practise with it regularly
You're also at the mercy of your guild. Kill it quickly and have good hero + pot uptime, or hope you can get an extra set of CDs in. Fight length makes a big difference.