You can thank to phenylephrine’s placebo effect for your improvements:
https://pubmed.ncbi.nlm.nih.gov/19230461/
Note: Some people do feel better on placebos than on nothing. It’s a quark of the human brain. So, if it’s working for you, don’t switch. Or, maybe try pseudoephedrine and feel even better…
I wouldn’t consider a consumer-grade router that doesn’t have OpenWRT support. No arbitrary EOL to worry about. I was very happy with OpenWRT until I moved to OPNsense router and Ubiquiti access points. I still use it on my travel router, too.
Edit: Check if your current router is supported by OpenWRT and get more life out of it.