As stated, Kirby at 170% with a fully charged F-Smash that lands the final hit can't possibly NOT kill him. What you're implying or playing isn't the full story here. After going into the training stage, even all the way to the right at 40m (we'll call it meters because whatever), and Kirby at 135% damage before a full charge F-Smash, he died. Your description doesn't fit any logical sense unless he teched off a wall/ceiling which is 100% possible.
Likewise, Cloud at 70% damage with Kirby's Down B does enough damage to launch him a bit but not high enough for a blast zone as he only goes upwards at MOST 15m and sideways about 8m Both of these are not high enough damage to kill from a blast zone or far enough to be irrecoverable. Once more, what you've stated is not enough to give any type of accurate representation of your real situation and is likely misleading due to personal reasons or something else.
To finish off, this is all with spirits OFF. If spirits were on for you, then anything you have to say about kill%, damage done, and taken are completely null and void. Spirits are not counted towards any regular smash matches since those not only vary massively from person to person, but also enemy CPU's and also dependent on if you're in Adventure Mode or what. Too many variables and the like.
TL;DR- I tested everything you had to say and unless you are playing with Spirits on, then everything you've said about kill% and such are completely inaccurate. Cloud needing a buff based on these stats (which he actually did have a nerf so I hear) is not valid.