I respect your opinion. In fact I used to share your view with respect to the old and new covenants. However when I began to study this subject for myself instead of just accepting what I was taught, I began to notice discrepancies.
You might want to reread Matt 5:14 as it states that not one jot or tittle will be till all is fulfilled - refers to heaven and earth passing away.
"For truly I tell you, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished."
Since heaven and earth still exists, the law in its entirety still exists Given this, the new covenant and the old covenant exist simultaneously. The primary difference is that the old covenant has now been made obsolete by the atonement. However what most fail to distinguish is that obsolete does not mean abolish but means out of date. For example, I can purchase a brand new car this year but by next year 2021, it will be made out of date by a newer model; however my car still exists and I still use it.
Heb 8:13 illustrates this.
In speaking of a new covenant, he makes the first one obsolete. And what is becoming obsolete and growing old is ready to vanish away. ESV
This verse is a peculiar one because the Greek word for obsolete is rendered in the perfect tense in the first sentence and in the present tense in the second sentence. The Greek perfect tense indicates a completed action but the results of that action continue on. The Greek present tense indicates continuous action. Thus in this verse the old covenant has been made obsolete (completed action) but the results of that action continue on till this day. That is why the second sentence in this verse states: is becoming obsolete and growing old.
The law has been made obsolete by Christ's atonement (a completed action with continuing results) but its effects are still being felt today as it is becoming obsolete (present tense) and growing old (present tense). Thus the law is ready to vanish away but has not - until such time that heaven and earth pass away.