TBF wires are always the best solution. I keep telling this to people who start similar threads about Mac Mini bluetooth issues, but bless 'em, they keep battling on like troupers, trying to make what is just a low-range weak radio signal work for them when the design of the Mini inherently compromises it further.
I once had similar issues to you with an iMac in the previous house I lived in, but it was because the airwaves were so crowded. I lived on a typical English street corner in a densely-populated area, and on a bad day my computer could detect 19 different wifis, all 3-5 bar strength just like my own. Trying to get my computer upstairs to connect wirelessly to my router downstairs was like trying to hold a meaningful conversation with your mate at the opposite end of a loud rowdy pub, late on a Friday night. To save me from ripping up the floors and installing cat cables everywhere, my solution was to use powerline adaptors.
Just realised my comparison with my 2010 Mac Mini is probably irrelevant because it likely only has 2.5gHz, which possibly had no (less) issues with the Mini design.