Looking for Jungle and Top Lane tips

While I do my best in every game, even when I have to fill, having played League for over a year now, I think I've found my niche as a Jungle/Top lane, and being rather aggressive one at that. I'm also pretty good at support, as I am decent at chaining cc and facilitating kills for the carry. That being said, I recently got demoted from Bronze I, no less. I began thinking that I was in "elo hell" which is very easy to do at my elo. It seems like no matter what I do, my bot lane always loses, and no matter how tanky I get as a tank jungler, no matter how much cc I put down, no matter how many kills I get (or feed to the carry), I just can't seem to pull the team out of the nose-dive that comes with a fed enemy carry. I can't even seem to prevent it either.

So, here I am looking for tips on how to become a better player, because I have to assume that my losses are my fault in some way. I got myself demoted by losing like... 10 games, so clearly I can't be that unlucky. I'll do my best to outline how most of my games go. I've been reading a lot of threads and lists, but I haven't been able to find one centered on bouncing back from a horribly thrown bot lane, which appears to be where the problem stems from.

I have had a lot of games recently where I would jungle Sion. I'm kinda stuck with maining a certain champion per role until I get the ip to get more champs to master; I did hit 30 rather recently, and I don't have a ton of champions to pick. Sion is my main guy for jungling, and top lane if we really need a tank. And I do fairly well in the first 10 minutes or so. I'll clear my jungle completely, have enough hp and mana to gank for bot (usually) and often times, my team will get first blood, and my carry (when bot is getting too much pressure) usually gets a double kill, a kill and an assist, or first blood and an assist. Naturally, this doesn't apply to every game; sometimes bot seems to be doing fine so I focus on lanes that need it more. But at around 10 minutes, it's like the entire bot lane forgets how to play league. Half time we've already taken first dragon after I gank because the lane is pushed. Then out of nowhere, the enemy carry will get double kill after double kill. That isn't even mentioning the games that aren't as rare as I'd like to say where the enemy team demolishes my bot lane before I can even clear my jungle. I mean, I can come in and gank and chain some cc between chilling smite and like... all of my abilities, but I can't stop my AD from being stupid and getting themselves killed when I'm halfway across the map with no boots, no teleport, and half the level of the enemies I'm trying to kill.

That being said, team fights later game are an absolute nightmare. No matter what I build, focusing the enemy carry does not work well for me, and focusing anyone else keeps me from doing my big job, absorbing damage for other teammates, and interrupting the enemy team. Most of the team fight, I'm dead because the enemy AD is so fed. As for trying to prevent this downward spiral, I try to keep morale up in chat and give advice (e.g. focus the enemy carry when everyone insists on attacking Alistar with his ult up)

I farm up, after all Sion's camp clear is really good, and I usually clear any given camp in under 30 seconds, which I'm told means that my farm is great. My ganking seems to be on point, and I seem to be doing pretty well with securing objectives, what could be the problem here?

As for tips for top lane, I'm also trying to find a way to go top, do well, and share that power with my team. Mobility is a pretty big issue for me on top (I'm not as good at top as I am jungle). Even with teleport, TP can leave me on the opposite side of the map while I roam, with Renekton taking tower while I try to get back to lane. It's less of a problem when I get really fed, because then I can just pick up a kill/assist from mid at pretty much any time, but how do a lot of people deal with the problem of top lane being so isolated?

Any advice is very much appreciated; I understand that this is a tall order, not being given any replay footage to actually SEE what's going on rather than me just describing it, and having to formulate advice from that. That being said, feel free to ask questions about things I haven't brought up or thought to mention. It could be what's holding me back if it didn't even occur to me, lol.