Mark I do understand your concern, and it's an indicator of the love of God working through you because you care about the lost.
I don't believe they are at any greater disadvantage than anyone else. We do all have an equal opportunity to seek and be found by the true and living God.
I'll explain.
I was brought up that "going to church" was the right thing to do, yet I was rarely taken except for "special occasions," and was told Bible stories as a child, at home and at school.
Interpretations were put upon them, I was fed reasons to not believe them, I was afraid of God, I doubted His very existence. (Funny thing that - we can fear what we don't think is there!

)
I saw that religion didn't work for most people I met who went to church, and found other spiritual paths more interesting.
Most people my age in Britain would probably be in this situation, and anyone a bit younger would not even have had much Bible fed to them, since fewer parents now attend church and fewer schools have even a nominally Christian assembly.
I would guess even the very few Brits, (maybe 5% or so - anyone got a statistic?), who have saved parents might still be immersed so deeply in our anti-Christ culture that they'd struggle.
I am astounded anyone makes it at all, but God is so longing to reach all.
He reached me, and it took many, many years for Him to break through my unbelief, fear and religiosity. I am a very slow learner, but He is patient.
Finally I saw that Jesus is God, prayed to Him to rescue me, called myself a Chrstian, but still it was several years before I grasped that I had sinned!
I knew I was " a sinner" but had zero comprehension of my own personal sin. I still thought I wasn't that bad a person!
I prayed for forgiveness without being specific, and didn't face some things until about 5 years after that first prayer. Always knew something was missing, but as I said, I can be slow.
A Muslim or Hindu
might even have a little head start over the atheist or the "church-goer" since they at least acknowledge spiritual possibilities.
They may have an awareness of the disatisfaction and limitations their religion, laws and restraints leave them with, and long for reality - the greatest thing Christians have is forgiveness, and they simply cannot find that in their faiths.
In the end, when we all see the full story,
nobody on Judgement Day will think God is unjust, and that truth will be acknowledged by all atheists, false faith followers, and religious church-goers who never longed for Jesus Himself but were content with their observance.
God bless, love Sue