The problem is that this question ultimately hinges on a court's judgment, and they can't know in advance what evidence of "reasonable defense of their trademark" will satisfy all the judges in all the cases where this issue is examined.

So from the trademark-holder's point of view, the approach has to be to do everything they can to be seen by the courts to be doing anything necessary to defend their brand; particularly for such a big/valuable brand like Hugo Boss, it's too risky to do anything less.

When you talk to people in these kinds of companies privately, they don't personally care at all if some largely-unrelated small business somewhere has a name that is vaguely reminiscent of theirs, and they'd rather not have to waste time and money taking action against them.

These indignant reactions always happen when a big corporate is seen to be bullying small, defenceless companies over trademarks, but on this topic it's a case of "don't hate the player, hate the game".