If you mean it's too slow to route over WiFi, then yes. 802.11g is not good for streaming HD video. But a wired connection of 100Mbps would be perfectly fine for HD video (probably not 4K, though).
Yes, that, but also that even the wired connection (and especially the WAN port) has become too slow to route the traffic at the speed the internet provider is actually providing it to you. If I were to still use my D-Link DIR-655 router, which I liked very much, there's no way I would be able to do 130 mbps down with it.
You're right, that's still enough for HD streaming, but I really don't want my own equipment throttling my bandwidth.