[Coda]

Somewhat. A good router can help improve network stability, although the connection speed might degrade in the process. However, as you imply, it can't do a whole lot if there's not a lot to work with, and it IS better to downgrade your service contract than to pay for service you can't get. IIRC they're actually not ALLOWED to sell you a package if they can't meet the guarantees by federal law, so if they can't get it working they're obligated to adjust your rates.

That said, you can't judge the connection quality based on wifi performance. The best test is to use Ethernet so that signal interference doesn't mess with your results.

It should be noted that Internet in apartments ALWAYS sucks because of how things are wired up and how many people are using wifi spectrum in the area. There's no two ways around it; during peak hours there's going to be congestion on both the wifi spectrum AND on the cable lines themselves.