Yes, lacking in early childhood experiences could include a lack of a formal preschool experience.
And YES, lack of experiences that could be taught by a parent can be addressed through intervention in school, and perhaps for some, an earlier start in a preschool setting.
However, whether we like it or not, the truth is that as a society we have been failing for many generations. We have produced adult children that do not have life skills, let alone parenting skills.
We all know that children need to be exposed at an early age to a stimulating environment. This does not have to mean expensive toys or trips to exotic locales. A family life rich in verbal and non-verbal communication is key. The greater the vocabulary of the parent, the greater the vocabulary of the child. If a parent speaks properly and clearly enunciates their words, speaks in complete sentences, and uses proper terminology, so will the child. If a parent reads, a child may follow by example. If a parent is sociable, a child may follow by example. It stands to reason that an unsociable parent will be more likely to have an unsociable child. However, being an introvert does not mean we cannot use and teach proper social skills.
If a child has not experienced group play, it will be another skill they will have to learn in the school setting. If they have not learned to communicate and share, that is another area they will need to cover - while simultaneously attempting to absorb everything that children who already have those foundation skills are learning.
It is our job as parents to prepare our children for life from the moment they are conceived. People need to step up to the challenge of raising their children according to the way for them, instead of expecting that others will do it.