What do you mean by difficulty attaining five stars?
Personally I found it really easy - it's a simple case of add more dinos to achieve the 5* dino score, then place enough hotels, shops, emergency shelters and weather stations and that's about it?
I think it would be better if Frontier could implement difficulty levels for the campaign - AND also make the rating more in line with the type of park you (or the division heads) want to create. E.g. if we choose a 'focus' then the requirements would be different. For example I made an amazing landscaped natural looking safari-style reserve in sandbox but this only got me about 3.5 stars because I didn't want to 'ruin the landscape' with buildings. If we were first able to choose the focus, perhaps the requirements for a 'safari' style them would be more about the dino requirements and less about the guest satisfaction. Or vice-versa you could choose a security focus and then it's more about shelter coverage, breakout rate, storm defence, guest fatalities, reducing outages etc. And then obvs the entertainment resort style park would need a balance between guest satisfaction and dino rating. Something like that?
For me it's more about having different ways to get 5 stars, rather than making it easier?