FLR(FP) as a spouse of UK citizen

I filed FLR(FP) application as a spouse of UK citizen over a year ago. I did Biometrics and the processing fee was taken. There is nothing complex in my application. I married to UK citizen and have our small UK citizen children here in the UK. I provided all required documents. The reason I filed FLR(FP) instead of FLR(M) is because I had a short term visa at the time I filed application.

What is an average timescale for processing this type of application? I know that there are no official timeframes imposed on Home Office to process FLR(FP). Does that mean that they can just do nothing for years? Home Office claims that that type of applications are extremely complex and thus take long time to process. But it is only partially true. Since April 2017 FLR(FP) applications can be processed on same day at Premium center for £590 extra fee. Not all of applications get processed on same day but certainly some do. Applications filed before April 2017 cannot be switched to same-day service unless you withdraw and lose your status. It is extremely unfair considering I did not have a choice when I filed my application.

Is there anything I can do? It is unbelievable how long it takes to process such a simple straighforward application.