Nope, League is an ever evolving game. They are forced to change champions to keep their game modern and good. They couldn't just leave Poppy or Taric or Sion as they were because they were shit, binary and boring for most players to play with and against. It's not fair to them that, for your benefit, they must pour resources to change something to keep ratings average (So already we have a situation where they are increasing expenses for the purpose of keeping revenue even. i.e an efficiency loss) on top of having to offer refunds to anyone who doesn't like their new work?
Also, even if you play 1 champion from the moment you download the game until the moment that champion gets a rework, it's not "your" champion. We as players don't get to pick what champions are "ours" and therefore dictate special treatment. Because if they grant your refund for your main, they have to allow ANYONE that asks to get a refund for that champion. Riot didn't rework your champion. They reworked their own champion, and it's up to you whether you continue playing it or not. It's an ever-evolving game, and as much as we all want to keep our cheesy AP sion builds and DFGarens, the reworks they do are a response to public outcry. Your champion is being reworked because your fellow players asked for it. You don't get a refund because you don't like it.
Also, Riot wants to encourage playrates for new content. Mains of a reworked champions are some of the best subjects because they know how that champion is meant to feel, they can properly identify the key differences and key playstyle changes more than regular players. They don't want Sion mains looking at the new kit, not seeing retarded AP ratios and CC, and just dropping the champion. They want you to play, look at what is good and what isn't in relation to old sion, and see what parts of these arguments hold validity. Mains complaining Sion couldn't off build an essentially counterplay-less cheese build mid anymore and have had their fun ruined weren't taken seriously. Those that identified the change in tankiness between old sion passive-health stack-shield-ult and new sion shield-healthstack and how the different CC changed his playstyle were.
I use Sion because he was regarded as useless until rework. Then all of the mains came out of the woodwork hating Riot for ruining their AP mid fun. If you weren't around for old Sion, good. It was just a one-sided laning phase.