Matthew Spriggs said those tasked with protecting Archie favoured Archie's mother Lesley Speed - who used a cushion and a scarf to smother and strangle the youngster - because she was a woman.
Jurors at Birmingham Crown Court unanimously convicted Speed on Monday after hearing how she was found with cuts to her neck, having killed Archie on the day of a family court hearing.
Speed, of Rushbury, near Church Stretton, had denied murdering Archie on September 21 last year, in the midst of a bitter custody battle.
In a victim impact statement read to the court, Mr Spriggs said of his son's murder: "The true horror that myself and my family are continuing to suffer is truly indescribable.
"The role of a parent is to protect their children from harm. To put the child's life and happiness above their own.
"I did all I could to protect my son but was denied the support I needed to do so."
In a lengthy statement read to the court by prosecutor Sally Howes QC, Mr Spriggs said he had a truly special bond with Archie, who had an "awesome" sense of humour.
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Mr Spriggs' statement continued: "There is something wrong with a system which allows one parent to dismiss legal proceedings without consequence and an even bigger problem when despite laws on equality, the assumption is that a mother must be 'good' and a father 'bad'.
"There were so many failures and missed opportunities to safeguard Archie but because the concerns were raised by myself - his father - they were dismissed.
"One person committed this heinous act against an innocent little boy but others were also complicit. Archie's death could have been avoided. He should be with me now."
The killing had robbed Archie of his childhood and his future, said Mr Spriggs, who described his grief as unbearable.
Speed, who watched and listened to the court proceedings via a videolink to HMP Foston Hall in Derbyshire, was being sentenced this afternoon.
Defence counsel Rachel Brand QC submitted that Speed had suffered from a depressive illness for several years, which has led to a "distorted and negative" pattern of thinking.