It's not about the logist here. The point is that on a mirror, with a "lucky" hero or a "lucky" choice of direction, it's many times harder to make a comeback because there are simply no other advantages to draw from. For this reason, M-mirrors are completely unplayable.

When talking about the ratio of "balance between HL+U and mirrors," I am relying exclusively on the experience of games played. In total across WT+SoD+HotA, I have likely played more mirror maps than any other currently active hero players. Including many series against top players. And so, simply by statistics in these games, there is a noticeably lower win percentage due to "layout" than on any other template. One-sided stomps on mirrors account for less than 20% of matches.

p.s. M-mirrors are obviously pure fun; I'm not touching those (skirmish etc.).