Ok, what does this have to do with poker at all? There is so little luck involved with real poker that its actually mind numbing how much effort people put into it to play it professionally. There are bad beats of course but the understanding has always been this. This is the big secret to league of legends, to poker and a lot of other similar mental sports.
If you make the correct decisions as often as possible and bring the odds in your favour, even by 1%, then over a large quantity of games you will come out ahead.
Your KDA and other numbers being the same on that account doesn't say you are playing on the level of your plat account. It says you are playing much WORSE. You are only able to achieve in silver right now on that account what you achieved in plat on your main. If you maintain a 3 KDA in Plat and cant get better then a 3 KDA in silver then there is something wrong in your ability to convert your experience into practical climbing ability.
I feel like there is a lot more to say about the whole luck of the dice thing with teams and its all bull shit. Here is another mind numbing prospect. Your mid laner who you noticed making a bad play? He isn't Bjergson. Actually, you may never be able to recognize that you were playing with a professional player in some cases if they weren't streaming. Even now professional players screw up all the time and if all we caught is the one missed ability many people would just condemn them for being shit lords and scream about the poor matchmaking if they didn't know who it was.
How many times do people go into a game and think something like, "Wow, everyone is so shit, no one has any mechanics!". It's silver. Of course no one has any mechanics. If everyone executed their champion like faker, no one would give a damn about those players. Believe it or not, you need to EXPECT people to fuck up in these games but we can't condemn them for it. At the end of the day we are so focused on how shit our team is we probably didn't stop to think about why that Yasuo didn't ult your perfect 5 man Gragas ult 2v5 or that maybe it was better that he didn't.
At the end of the day, if you really are a plat player raising a silver account, it will get plat eventually too. Give it time and stop looking for reasons outside of your own play to justify losses. You proved you can do it once, you can do it again.