Is a Japanese sword so delicate that a botched cut could actually damage or even destroy it? It seems that in actual combat, with armor-wearing soldiers, and the chaos stemmed from weapons of all sort getting thrashed about, you must assume that the weapon will take some level of abuse. So could a botched cut on tatami mats really be so dangerous to the weapon?
It depends.
One can not just categorically lump all "Japanese Swords" together when it comes to questions of performance.
But - historically speaking and even today with production katana or custom ones - you will find that the quality varies.
In general the ability of a given blade to withstand the inevitable 'bad sword day' that everyone eventually has is mostly due to the quality of the smith's heat treating of a blade.
It has less to do with the steel used - so just because a maker claims it is tamahagane, L-6, or 1086, or 5160, or whatever - means less than the reputation of the smith who made it.
In general, when speaking of modern production katana specifically designed for cutting (wide/thin blades) then,
in general, they will be more prone to bending than say a blade with a more traditional shape that is not as wide, not as thin.
In general, the consensus of most practitioners I've talked to who actually compete in cutting events, and to polishers who see these types of blades quite a bit - is that,
in general, for the SAME blade, the one with bo-hi will bend easier than the one without bo-hi.
But - that is not to say that just because a blade has bo-hi that it will be easy to bend. Which brings us back to who made the blade, how good was the heat treat, and to some extent the geometry of the blade in question - all factoring together that could result in a blade WITH bo-hi that is NOT easy to bend.
It depends - but a good quality blade made by a skilled smith with a quality heat treat will not be easy to bend.
Bear in mind - that ANY blade can be bent - there is no such thing as an indestructible blade....yet (even the L-6 blades by Howard Clark can bend or chip - just under extreme conditions that you will not likely encounter in a typical cutting environment).
YMMV,
Erik