Yes, you can reach higher states and if you reach enlightenment without a teacher that means you're a paccekabuddha. The appearance of a pacceka-buddha isn't that uncommon and many can arise at once.
It seems that paccekabuddhas usually encounter sammasambuddhas in some past existence and have developed certain kamma.
The majority of people regardless of what they try won't be able to reach certain states without a teacher because of their kamma. The majority of people I encounter do sinful deeds unknowingly and think of themselves as good people.
The practice of metta (loving-kindness) seems to be only slightly below the achievement of the jhanas so if having difficulty with training then practice metta, virtue, and generating good kamma.
“Bhikkhus, whatever grounds there are for making merit productive of a
future birth, all these do not equal a sixteenth part of the
mind-release of loving-kindness. The mind-release of loving-kindness
surpasses them and shines forth, bright and brilliant." (Iti 27)
I'm not sure if the arahants disappeared but I feel that they did around the same time predicted (500 years after the parinibbana).
Without arahants, paccekabuddhas, or a sammasambuddha existing in the world the dhamma is lost.
The time-period we exist in now is more fascinating than ever because higher mathematics and the scientific method exists now (since around the 17th-18th century, it did not exist for most of history).
So if a fully enlightened being arises now and people question him it will likely shock everyone.