I will start with the middle issue.
“Mesirah” was not the outcome of “fear of severity” by courts outside the Beith Din, not at all.

Jewish courts were not an expression of some “siege mentality”, a most fallacious consideration/comment.

The institution of communal, Jewish Beith Din in the old continent was a privilege afforded to Jewish communities by the non Jewish authorities, be it monarchic or just urban/ civil. From Netherlands, Italy to Germany to Lithuania, traversing Moravia and even Hungary, as early as the 16th century, Jewish community were given the requested RIGHT to administer their religion in its fullest expression, practicing and institutionalising chalacha being pivotal in the proper function of Judaism. This was based on the well known principle of “Dina’ de-malkuta’ dina” ( obedience to communal norms as well as Jewish law ) which I am sure you know too well.
In most cases there were allowed even TWO courts, one lay , lead by “manhigim” and one religious, with the famous “dayanim”. Divergences were quite common, but generally the system worked pretty well.
True “mesirah” was a indictment,however, it was an acceptable/approved charge by non Jewish authorities, as they were fully aware of its meaning and subsequent punishments rendered by the Jewish courts. The purpose was not to defy or deny justice but to protect the very authority of the same Jewish courts granted authority by the same non Jewish authorities. It confirmed to the Jewish legal fora their rights as granted by the non Jewish authorities. Jewish judicial structures were, in some case, so large that there were Jewish super-communal Courts at the level of the Provincial ( Jewish) Council of Lithuania, or the Council of Four Lands as early as 16 and 17 centuries. Some courts had prisons of their own and among the punishments allowed death penalty was also on the books !!! Excommunications were also allowed !!! All these were with the express approval of the other “parties” in that “dina’ de-malka dina” concept !!!
The main issue is that these institutions were not an expression of Jewish “severity” in a state of “siege”, but the very concrete, the very tachles of consolidation of Jewish continuity, by far the greatest “allowance” within the concept of degrees of tolerance of a non Jewish society. Persecutions notwithstanding, if Jewish principles/spiritual content would not have been allowed to be practiced and those courts were by far the most reliable institutions for this purpose, there is no doubt that Jewish life/communities as we know them today would have been gone/assimilated into oblivion. To this extent it must be noted that, with the advent of haskala, the very institutions of Jewish judicial courts were seriously challenged and denied legitimacy from within the Jewish fold.Here one may recall the saying that it is very rare to find a third – I’ll grant you “fourth” – “haskala type” Jewish generation. This means that Jewish law , as practiced by the known Beitei Dinei are integral to Jewish identity and continuity.
We may also discuss later the individual authority of a posek within the system etc.
I am very proud that my great-grand father, Josef Spira was the Mayor of the Jewish “township” and manhig of that cute little Moravian town Trbic and also , just around the corner in sub Carpathian Slovakia, my other side Grand father, Rabbi Jozsef Grunfeld came from a very, very frumm lot of dayanim in Kiraly Helmec. I am saying all this as I am fishing for mishpuha among those anxious to be related to me……