I disagree with the premise of Landmarkism. Looking for an unbroken continuity of a physical Baptist Church (or any church, for that matter) makes the same error as does the RCC. This is not the nature of the Church.
Except that is not the premise of Landmarkism.
In his book "Old Landmarkism, What Is It" J.R. Graves states the "marks" of a Landmarker:
1. The church of Christ is a divine institution.
2. The church of Christ is a visible institution.
3. The church of Christ is located on this Earth.
4. The church of Christ is a local organization, a single congregation.
5. The membership of the church of Christ are all professedly regenerate in heart before baptism.
6. The baptism of the church of Christ is the profession, on the part of the subject, of the faith of the Gospel by which he is saved.
7. The Lord's Supper was observed as a local church ordinance, commemorative only of the sacrificial chastisement of Christ for His people, never expressive of personal fellowship, or of courtesy for others, or used as a sacrament.
Those seven "marks" delineate what Landmarkism originally was. Today some have added and added and added to what a Landmarker is, but those additions, much like the additions to the fundamentals of the faith (no pants on women, KJVO, etc.), have nothing to do with true Landmarkism.