You might be surprised by what counts as “normal treatment” for hold luggage. It all comes down to how you packed it, the mere fact the glass was broken really does not prove anything out of the ordinary happened. But next time you travel, fully expect your luggage to be thrown around, turned upside down several times, fall from one conveyor belt to the other, hit other pieces of luggage, be stacked on a cart with four-five heavy bags on top of it, etc.

Beyond that, I don't know what your legal standing is but my personal experience with low-cost airlines (including easy jet) is that they will keep you in a holding pattern with boilerplate answers and are even less helpful than legacy airlines (which could offer you something, not because they are liable but simply as a commercial gesture). The problem is that escalating things beyond an email (e.g. hiring a lawyer) is likely to be too costly to make sense.

One last option is to turn to social media. Airlines are sometimes more responsive that way, to avoid public shaming.