Well, I'll be honest I had a much longer and more well thought out post written but I accidentally refreshed page and as I don't feel spending another hour or so I'll try and keep it brief.
The issue with old trundle wasn't that his story was finished more so as what the finished product was after the story. Trundle had no reasons left. Tribe dead, a cure being lethal. Not only is the entire Bio thrown out the window because of the judgement but it also left Trundle as nothing more then a grumpy Troll. Honestly the way that judgement ended he could've just as easily walked out of the institute and never show his face in Valoran again. And that was why the took another crack at trundle. They didn't replace him as you say but Riot genuinely tried to do Trundle right, old Trundle's stories were fundamentally flawed. I'm not saying new Trund is perfect but I know it's a lot better.
Secondly new Trundle and old Trundle are the SAME trundle. If you look at the core of the stories both new and old you'll see that there's very similar core in each.
Both new and old Trundle have bad governors. New with the foolish chieftain while old trundle had the Sages of the tribe that erroneously wanted to rid the plague from their people.
Both new and old Trundle's were disrespected by their kinsmen New trundle being openly mocked for challenging the chief while old trundle was bullied.
Both put their lives on the line for their people. New trundle with the risky journey to find the weapon he spoke of while the old Trundle took the burden of the plague.
Both return as heroes, New trundle with the weapon and old trundle allowing for his people to be freed from the plague.
The only 2 changes at the core are important improvements that makes New trundle's lore so much healthier. 1st He now is connect to Lissandra, another champion. Before we never saw Trundle interact with another champion, and weren't even lead to believe he would have any drive or reason to do so.
2nd instead of killing off his entire tribe like old trundle did by not giving them the plague back but instead new trundle kills the foolish leaders alone, and leads his people to greater heights. Make no mistake, he does this for his people, his lore states he fears what would become of them if they were lead by the chief any longer.
So same story at the core, just an ending that open's doors for him AND his people, rather then closing them.
If is for this reason I just can't understand why you would supposedly enjoy Old trundle's lore, yet turn your nose up as a new one when I've clearly shown how similar they are. This statement will be hyperbolic and I'm sorry if it offends you or other's but to me it feels as vain and wrong as no longer wanting to be freinds with someone because they had a sex change operation.
It's the EXACT same person, but because the package is now wrapped differently you reject it. I know you're entitled to your opinion but I simply cannot see it in such a way.