You have made several mistakes in your post, I will highlight them so that you can see where you went wrong:
1) David Cameron's reason for joining was: “The longer Isil is allowed to grow in Syria, the greater the threat it will pose. It is wrong for the United Kingdom to subcontract its security to other countries, and to expect the aircrews of other nations to carry the burdens and the risks of striking Isil in Syria to stop terrorism here in Britain.” It was not as you seem to think only because we alone have Brimstone.
2) The Brimstone was mentioned during the Syria debate as a direct answer to a question of how we might minimise civilian deaths or collateral damage. It was not as you seem to think the reason that we joined the coalition. But a tool that could be used if any when needed. It might be that a situation has not yet occurred where it is needed over another weapon and so it simply hasn't suited the RAF to use one yet.
3) It doesn't matter how accurate a weapon is - you need qualified targets to shoot them at. No targets may have presented themselves that required it.
It seems that the plan currently has Tornados (with the brimstones) being used in Iraq and Reapers and Typhoons being used in Syria (Reaper uses Hellfire which is similar to brimstone in some ways, Typhoon has Paveway)
It could be for many reasons that things are being used this way round - plane fuel use, endurance, time on target etc etc etc or perhaps its been decided that after the Turkey / Russia shootdown incident that the Typhoons are better equipped for contested airspace (and the Reapers are expendable)
4) The statistic from the article / Parliamentary question only targets a specific date range, Syria, and ISIS "kills" It doesn't include hits after those dates, in Iraq or strikes against non human targets.
This question shows that they have been used in Syria, upto 18th Jan, 5 had been used in Syria (I am assuming from the answer to the other question that they must not have resulted in kills)
http://www.parliament.uk/business/p...ts/written-question/Commons/2016-01-12/903067
5) The idea that you are OK with us hitting ISIS in Syria as long as we use Brimstone - but feel disgusted, outraged and lied too because we are using other weapons is hilarious
6) Calling it an "illegal coalition" is the derpiest thing I have read on here in weeks (and I have been reading the trump thread
) so congratulations for that.