OK, so we now have confirmation that the hardware is OK and that OpenBSD is not the bottleneck in routing and filtering packets to your laptop.
One problem solved
There are 2 implementation of pppoe in OpenBSD, one is part of the kernel and the other one is in userland.
The userland one has the advantage that it is somewhat easier to debug, but it is slower because data needs to be copied from/to kernel space to/from userland.
The kernel pppoe is described in the pppoe(4) man page. It is quite readable and even gives an example configuration.
Give it a try. Just make sure you know how to revert your setup in case things don't work out
One warning, I don't use PPPoE so any efforts of my side will be completely theoretical. Or maybe somebody with kernel pppoe experience can give a helping hand.
BTW My daughter lives in Eindhoven, her appartment block has 100mbit up/down. Unbelievable fast.
I live about 25 km more to the southeast, 1 km from the Belgian border. The town government is trying to get people interested in a glass fiber connection here too.