I'm afraid I don't know a way of downgrading that hboot. To change hboot you need S-Off or an RUU. The RUU won't downgrade hboot, and the S-Off tool won't run on that version.
Radios suffer the usual problem of CDMA devices: you can find every GSM radio ever released in a flashable form, but I've never seen this for CDMA. Do NOT attempt to flash a GSM radio because that will be the end of your device if you do.
But before we get too carried away with the radio, the important question is whether your WiFi reception is really worse, or whether it just shows fewer bars than before? There is no universal calibration for signal bars, so the same signal may show more or fewer bars with different ROMs. The real test is whether it works the same, not how many bars it shows.
Edit: sorry, read it again and it says you can't connect. Can you see the network if you scan for it? I use a little app called WiFi Analyser to check WiFi signals. Just need to work out whether the problem is reception (may be radio related) or connection (more likely ROM or settings). I had a CM ROM become very finicky about connections once, and clearing all saved networks fixed it.