This really is bad form on Lenovo's part and to be honest and I know this is easy to say but I think a new machine albeit a refurbished one or what may be the way to go as you say going back to 8.1 would be a real pig of a thing to have to do. If it were me I would even think about going back to 7 with an OEM if you cannot afford another machine.
Just as a by the by you could run 8.1 in 7 mode with Classic Shell to do away with all that apps look but all the same it stinks. Classic Shell - Start menu and other Windows enhancements
and for what it is worth you can use this for 10.