What you dont seems to understand is that the only 2 stats that REALLY matter are Speed and Accel. Any other stat is literally just preference. You can have the lowest handling possible and still do fine on stages like Neo Bowser City or DK Pass. You can have terrible Off-Road and do fine at Kalamari Desert or Rosalina's Ice World. All you have to do is realize that you need to practice the stages and get over the learning curve when you back off on the handling and such. Learn when to start turns, practice your lines, etc, and any kart will work, but you NEED the Speed and Accel to stay ahead/keep up, and to recover from getting hit (no matter how good you are or how hard you try to avoid it, you WILL get hit).
Basically what Im saying is, you're overplaying how good the pieces are just cuz they have high stats. The good pieces have high stats IN THE IMPORTANT AREAS. Handling, Off-Road, etc, are all just luxuries. Build Speed/Accel, learn to use the kart, and thats the best option available. The only reason anyone would ever want to add in those other stats would be if they want to have a kart they can excel in without putting any work into using it. Those are the karts that are easy to use, but dont give you that 'Funky Kong mode' which lets you get and keep leads. The karts that WILL give you that Funky Kong mode in this game, you need to practice in, cuz they are harder to use. There arent any Flame Runners or Mach Bikes this time around, the good karts actually take practice to use. Take the time to learn in the good karts or go easy mode for less reward, your choice.