More than likely its exactly what you said, but with a balance. You were staying at silver 5 because of the safety net.
However low silver, nearly all of silver except 2 and 1, is insanely fucking random matching. The games are incredibly inconsistent. Its not hard to just go neutral and get carried every other game.... or lose 6 and then win 6. Riot tries to keep you at 50% too. I always found it would keep me about 10 games negative wins.
It is actually really difficult to get kicked out of silver 5. I've done it a couple times and then instantly got back into silver because high bronze matching is fine. The high bronze games are much much better than silver 5. MUCH MUCH MUCH BETTER. Like, getting into silver 5 feels like FALLING down the ladder into bronze 3. No joke. Its insanely bad.
Which is another perhaps piece of the puzzle. Its hard to know, but if you actually do know what you're doing- for instance do you see other players mistakes before they make them? There are a lot of monkeys in there, and many times they just make terrible decisions.
I've had sooo many times where the jungle has literally walked through wards, i've pinged out my support and i'm back at the turret, and hes still thinking i'm going to follow up on his engage. Sooooo many times.
In theory, if matching is actually equal chance per team to win... then you going even with your lane should mean you win more often than lose. Personally I feel like this is simply false. I've played way way way too many games of teams feeding their asses off to think that is remotely true.
Will the game try to keep you at a 50% winrate? Absolutely. Will the games be matched well so that you have a 50/50 chance to win, hell no. No fucking way.
More than likely you are better than you think you are, simply because you think you are bad- which means you notice your mistakes. So assuming that you learn and correct those, like you talked about, you shouldn't have an issue with climbing. However, I think if you play on one account, the system will never let you climb once you plateau.
I don't know what it is, but I know I'm far, far, far, far, far better than I was my first season- and I still can't seem to get past the fucking gatekeepers in silver. Eventually I came to the conclusion after climbing to silver 3 and then always getting a massive loss streak... that something is fucked up with matching. I consistently get games where I win 6, lose 6, I've studied and studied and studied myself. I know i'm playing consistent.
Meaning matching is fucked. I've started to see patterns in it too and talked to a lot of other players that experience the exact same fluxuations. I've tried playing lots of games, 1-2 games a day to make sure I wasn't tired or something. Doesn't matter.
Thats said, you will unquestionably improve by doing this. It just feels bad to not be in the elo where you belong, up or down.