Did you hear this from Tier 3 support? If so, I would be surprised. Tier 3 support normally have the tools and the skills to actually diagnose issues rather than just reboot the modem and schedule a tech visit if that doesn't work.
If you're dealing with someone that can't or won't help you, try asking for the case to be escalated, or hang up and call back.
You do not talk to Tier 3 support unless you put a ticket in to actually speak with them. Also they can have all the tools they want, but in the end they could have done that with routers as well. But they refused.