I’d broadly agree with this. It’s very easy to have a negligible religious group just by not trying to appeal to them (e.g. teaching evolution only, not having faith school subsidies, not having school prayer). I’ve definitely found they’ve disappeared in a short amount of time (one or two terms). I’ve only ever run into a problem with them becoming hostile when I’ve been actively propping them up with faith school subsidies and school prayer, but also doing stuff they don’t like (like unlimited abortion or stem cell research).
I think this is most noticeable with the religious group, but it’s a trend I’ve generally noticed, and I think contributes to the game feeling a bit easy. I can just decide I’m going socialist, and while it might upset some capitalists for a little bit, soon there just aren’t enough to matter. For example, the USA is the most capitalist country at the start (~45% capitalist, ~55% socialist), but after a term and a half that’s swung by 15% to around 30% capitalist and around 70% socialist. This is without me really trying to get rid of capitalists, and just putting in more socialist policies, and it ultimately means you’re not so much lead by the voters but the voters are lead by you. While I agree that should happen to an extent, and it’s nice to see, I think it’s just too much too quickly at the moment, to where it means that individual voter groups aren’t really important. The ones you’re pleasing grow and the ones you’re annoying shrink, and soon you just have a population that agrees with you and as long as you don’t break the country you can sail along at 90%+ approval.