Figured it out.
It was ISP-side problem.

Direct conection to ISP's fiber modem results same.

Atually, Very satisfied with HAP AC2 perfornance.

Much appreciated for the kind answers! @msatter @whatever

Wan on Ether 1 and PC on Ether 2. Link rate status of both interfaces are at 1Gbps with Full Duplex checked. The ISP guarantees 500Mbps speed. Speedtest.net and ISP-provided Speed test results are under 100Mbps. HAP AC^2 has been set automatically. What can i try or test to solve this issue? Thank y...

Yes, exactly thats what i want to do.

So, you says, it has to use mangle rule, software approach, right?

but RB2011 has 2 separate switch. Is not it possible to do it in hardware level?

There are Switch1 and Switch2.

Wan1 of Port1 on Switch 1, Bridge1 of Port2-5 through DHCP1 on Wan1
Wan2 of Port6 on Switch 2, Bridge2 of Port7-10 through DHCP2 on Wan2

Masquerade on each separate way.

I searched Raw examples but there are no examples yet.

Just wonder which one is faster.

Thanks.

+1 for IGMP Snooping with RB2011 routerboard.

Please, MikroTik. Please Please Please