Tp-link Archer C5 V4 low speed

So! Hi guys, my first topic, couple days ago installed openwrt on my device (tp-link archer c5 v4), openwrt is not really released on my device but as it said it works perfectly fine, except 1 thing.
My Stock Firmware speed provided by isp (PPPOE) 400/400 mbit, and it works great on stock firmware.
On Openwrt it works only 400/200, i activated Software based offloading for routing/NAT, i also tryed play with QOS/SQM settings but it gets as hell worse, when i stick it on 350.000/350.000 kbits it's gets down to 100/100 mbits! I played with both, QOS and SQM QOS tools, as it said on wiki (yes i read whole article before write here and disturb people).
I also checked dslreports, and yes, it says i have bufferbloats, but i really cant fix it.
Can any one give me advice?
(and if you have question, why i tryed openwrt, it because i wanted try something new, something smart. And sorry for my english, im from RU, and may have english language mistakes)

You're going to need a router with more CPU to run OpenWrt on a 400/400 line. What you have is a MT7620 chip with a single 580 MHz MIPS core, which is really not very fast. For this model TP-Link took an entry-level SoC and put a gigabit switch on it.

The stock firmware uses a lot of tricks to optimize for speed. But then it can only do simple things.

Hi! Thank you for such a quick response, can you help me configure this way, i have perfect 10Gbit/SFP Mikrotik, i can configure switch, but i have no idea how to configure router via openwrt? or there is some guide on wiki?

Should i just open my pppoe connection on router and plug switch to any lan?