I wonder how far out of the norm this is. I’d imagine the first line is usually going to have the most time and resources dedicated to it, but ignoring the fallback lines because “nah theh won’t breach it” is just stupid
It has probably less to do with ignoring the fallback lines and more with the fact that they simply don’t have the recources and time to build any kind of foolproof defensive lines. Their troops are stretched quite thin there and by strenghtening one part you’re just going to make the Ukrainians attack you elsewhere.