I myself have substantial experience with Protestantism as indeed I have worked as a minister within a major Protestant tradition, so I am extremely familiar with the fact that the major Protestant denominations are not greatly different from each other.
However, this also somewhat misses the point. The real problem is the proliferation of fundamentalist churches which are actually not at all friendly, but rather hostile to each other, which you probably have not encountered in the Czech Republic, except perhaps among occasional American missionaries some of them might send (some of them do not practice missionary work as they rather absurdly consider it to be unscriptural, for example, some of the more extreme Reformed Fundamentalist churches and also groups like some of the Plymouth Brethren in the UK, which are known for their deep suspicion of outsiders, and also many of the Mennonite and Anabaptist denominations, and related groups such as the Amish, in the US. And there are a large number of such groups, basically, very small denominations that are hostile to outsiders to the point where they function as cults.
But even if we consider the major Protestant denominations which agree on most points with each other and indeed actually with the Orthodox and the Roman Catholics*, which is the raison d’etre for the Traditional Theology subforum, that being the commonality between the liturgical Protestants, the Orthodox, and the Catholics, it is still extremely unfortunate that a state of full communion does not exist between them. For example, even among Lutherans, one cannot be a member of WELS and partake of the Eucharist at an LCMS church, or vice versa. Indeed WELS is somewhat notorious as they will not even pray with members of other churches except for, if I recall, a small number of Lutheran churches with a somewhat Reformed theology that are in precise doctrinal agreement with them, which is in contrast to the LCMS which is somewhat more open to ecumenical relations.
*and here is a fun fact: the Orthodox Church of the Czech Lands and Slovakia venerates as saints St. Jan Hus and St. Jerome of Prague, who are also the founders of the Moravian denomination, at least in part (although the Moravians of today, in the US at least, are most influenced by the doctrines of the German pietist Nikolaus Ludwig Graf von Zinzendorf, the Count of Zinzendorf, who settled a surviving remnant of Moravians on his lands in Saxony to escape persecution by the Austrians.