no, it's a througput to the router host, not switching at all
cuz router cpu loaded by packets generation in this case
1gbit port can archive 2gbps throughput in theory, 1gbps incoming and 1gbps outgoing simultaneously (full duplex), and mt7621 soc can reach such throughput (2gbps duplex) when both rgmii's (ralink gigabit media-independent interface(mii)) are connected to the internal switch (1 rgmii=1gbps, 1 rgmii for incoming and one rgmii for outgoing traffic)
but in case of witi - second internal rgmii interface is used for external gigaphy (wan2) so only 1 gigabit in full duplex can be utilized with only one rgmii (no matter, wan or wan2 port), the only exception - my firmware, where rgmii interfaces running in "turbo" trgmii-1200 mode with 1.2gbps (instead of 1gbps) throughput limit.
openwrt mediatek soc support is aweful atm, it's not optimized and don't supports PPE block
optimized firmware will give you SATA throughput near the limit of gigabit interface