Not getting 300mbps on Ex2700

Your EX2700 seems to have a good link to the primary router, but it does run this link on 144 Mb/s link rate only. This does also limit the maximum possible link rate of the EX2700 access point which does run on the same radio and therefore the same channel like the primary router.

First item to check is if the Virgin media router 2.4 GHz wireless can be reconfigured to 40 MHz (20+20 MHz) bandwidth, this should allow the EX2700 operate the link to the primary router on about 270...300 Mb/s, and it will serve the EX2700 access point on up to 300 Mb/s, too.

Next check the signal level (quality) on the computer or gaming device. Relocating the EX2700 a little bit more towards your room might help.

Please be aware that the physical link rates can't be reached in the effective throughput. However, in your case the 144 Mb/s (assuming the computer or gaming device should sync to about the same number) only 10 Mb/s throughput not ideal. In a similar application, the EX3700 (similar tech on 2.4 GHz as the EX2700) does run in the 15 .. 35 Mb/s range. Here however we have massive traffic on air in the 2.4 GHz band from two Arlo systems, so (massive) interferences are predictable.