I thought 1.7Gb possible? This is what I was told when asking why I get 515Mb at my hub and only a max of just over 300 at the primary disc:
The Whole Home Wi-Fi is limited to 300Mbps at primary or any disc connected by Ethernet and the speeds of any Wi-Fi discs will be less.
1733 Mbps is a theoretical maximum data rate for all wifi data streams combined across multiple devices in 4x4 MIMO. You won't see anywhere near that on any one device and real world numbers will be well below that.
I read that your disc is connected by ethernet cable to the Hub, but how are you determining the 300 Mbps? Is it using an online speed tester on a device that is connected via Wifi to the disc? If so, what kind of device is it? Mobile devices such as mobile phones, tablets, laptops will most likely be 1x1 MIMO or 2x2 MIMO and therefore, due to the technology, environmental factors (interference, congestion), overheads and losses, the best you could realistically hope for on Wifi 5 is probably around 300-450 Mbps on any one device.
If you want to max out your 515 Mbps internet connection on single devices, then you would need to have those devices hardwired via ethernet cable or turn to Wifi 6 technology for the best performance.
That makes a lot more sense than there being a limit on the disc itself. Yes, I am doing the mesh-side testing from an Android/ms windows device so expected some losses. It was the c 200 loss that I thought looked odd. We only pay for 300 Mb that supports the number of people working from home or streaming so fortunately no financial/performance penalty (500 was applied as goodwill in respect of other issues).