Well, if your goal is to keep your current customers, and to attract more, unsatisfied customers should be your problem, whether you can do something about or not, and whether the problems are real or imaginary.

Fencer: Our power ends at the outgoing port of our firewall.

Yes...., but, where your firewall ends is something you can do about. If there's a network problem, and that problem is caused by your upstream provider, then you aren't entirely powerless. You could switch provider, or get a faster pipe. I'm not saying you should, or that it's wise business wise, just pointing out that just brushing it off with "oh well, nothing we can do" is a bit short sighted. If Disney had build Disneyworld at the end of a dirt road, and people would complain it's hard to reach, Disney wouldn't say "oh, but the lines in the park are short, and it isn't our problem there's only a dirt road to our park".

A website cannot control the speed of the Internet, but it can decide where it connects to the Internet.