Pi 4 slow wifi?

I've been having Slow Wifi issues on my RazPi on 2.4Ghz. This is local wifi in a small house. It's slower than anything else in my place atm. Things I've done include

1. Trying an update of the firmware binary brcmfmac43455-sdio.bin to the latest from the git of the kernel firmware. No help.
2. I noticed the firmware txt files were config files, assigning values to labels. There was one for the Rpi-3, one for the Rpi-4, and another for some weird name. The Debian stuff I was using just had brcmfmac43455-sdio.txt. I diffed that with the RazPi-4 one in the kernel git, and they differed. So I copied the RPi-4 file from the kernel git to my firmware dir as brcmfmac-sdio.txt. That may have gotten me a few % increase.
3. Researched the hardware, which was interesting. Cypress start their chip numbers with CY, and Broadcom with BCM. There was a Broadcom manufactured IC BCM43454 & BCM43456; But the only BCM43455 was manufactured by Cypress. The brcmfmac43455 runs the RazPi-4 wifi, but I presume it's an IP core (or a chunk of an ASIC design) in the APU, the BCM2711 SoC. The key factor here is that they're unlikely to have tested the hardware sensitivity in the BCM2711 core like they tested the one in silicon.
4. Researched my local problem. One of the things I tried was 'iwlist wlan0 scan |grep -c Channel' . The RazPi counted 20. As fast as I could get upstairs I tried it on the Laptop, there was 36. With 'iwlist wlan0 scan |grep -A2 Channel,' my Laptop (with an ath9k wifi) was spotting channels at >=-92dBm, or Quality 17/70. I saw basically nothing below 40/70 on the RazPi, so the sensitivity is low. That means channels it doesn't know about could be interfering with it. That could confuse things.

I'm running out of clever things to do here that yield any information. Has anyone any ideas for me? I seem to have taken it about as far as I can, and although my Pi was bought as a media server, It won't download fast enough to do that.