In the meanwhile I moved my docker to PC (Debian 10 on i3 6th Gen+16GB RAM+spinning disk). While the speed is unchanged with WiFi, with LAN connection I get much higher throughput. Browser transfer is >100MBIt/s for 1GB file and client sync goes over 500MBit/s (spikes to >800MBit/s). My conclusion is the problem is not related to Traefik itself as my tests proof it CAN handle faster transfers.
