No one is saying Monastic spirituality in church design needs to be imposed on anyone.
But you do realize that monastic orders were responsible for providing the clergy for many parishes, and they would have certainly influenced their churches. Many monasteries were also territorial abbeys that took the place of a diocese. There are still a few in existence; the abbot acted as the de facto bishop of the territory. In many places the monastic church was the de facto parish church.
Incidentally when it comes to catechezing, you’re right, artwork was used. Inside Subiaco abbey in Italy, many ancient frescoes tell the story of the scriptures, the saints, etc.; there’s a fresco of St. Francis of Assisi who visited there for advice prior to forming his order; it’s one of the few depictions of him without the stigmata. The earliest fresco there dates back to the eight century!
Monastic tradition is a valid tradition in the Church and there’s nothing wrong with it influencing (not imposing) their spirituality if the parish desires it, just as a parish may have Franciscan or other elements of spirituality expressed either visually or otherwise.
Inasmuch as plain churches represent a form of austere spirituality that has its place in the history and traditions of the Church, there’s nothing wrong with it as long as it’s done for the right reasons, just as there’s nothing wrong with a more traditionally ornate Catholic church if that’s the direction the parish leans and they can afford it.