I recently purchased an Archer T6E AC1300 WiFi PCIe Adapter from TP-Link and it has a decent signal, but only if the side panel is removed from the case (Phanteks P300A). The motherboard is ASUS Prime Z590 and all firmware should be up to date.
Try this in case it helps. You said, "both pointed as best towards new router as possible". The antennas do NOT send a directed BEAM out to their destimation. They send out a field that IS oriented in space. The idea here is that the antennas on BOTH the router and the PCIe card shuld be pointed in the SAME direction - usually, just STRAIGHT UP - so that their field patterns are aligned.