i see your reasoning too, seeing a champion just get crushed in one patch for counterplay issues (kassadin, veigar kinda, olaf) really hurts especially if you play that champion, but i think in the long run building them back up is the correct way to go. i think the problem is Riot right now tends to be slow to build champs back up or even sometimes just doesn't for a long time.
like remember what happened to olaf? he got nerfed super super hard and wasn't fixed for over a year, that really sucked for olaf players. and while i think riot is doing better then the past when it comes to follow up (veigar buffs next patch look promising) i think they can still be more speedy with patches, i'd hate to be a veigar main and feel like picking my champion is a hindrance to my team or something.
like what if they did their big patches, and then like a next week follow up patch with more mild number tunings to keep the damaged champion in the game. (like a patch 5.45 or something)
tl:dr i agree with riots way of fixing champions and not just undoing changes, but it needs to be faster so its less painful for players of those champions.