Ahoy! kudos on the win. Yet again I will be disagreeing with you and your analysis of that match thou buddy. I hope someday we will see more eye to eye on this lol.
So, your "**What I found the most suprising, was his KDA and CS. How did a platinum player end with a score of 12/17/5 and 120 CS in 20 minutes?" **makes it sound like the game lasted only 20 min and he only got 120 cs (inaccurate number and I don't know where your grabbing it from btw.) It was a 40 min game and he got 229 cs ultimately ending the game with more cs then you (202). Also his cs at 20 min was 109 and yours was 101, you got 1 cs away at 21 min but he got back the cs lead and never lost it for rest of game, the 41min gold time line has Lucian ending with a 100 gold lead on you still despite being on losing team. At 15 min he had 2k gold advantage on you. I don't think this shows you having made any real impact vs him in lane, and claiming credit for winning team fights is a stretch as well, as your numbers are not above your teammates. Where as Lucians teammates are not even near his numbers, velkoz support being the 2nd most positive player on his team. Xin jungle failed his team badly and was a level 13 account. Xayah farmed but only farmed, her cs was best in game but her damage to champs (job of adc) was under 20k. Dari was aight comparatively to jungle and adc but did not impact the match all to much.
So You lost in lane to him as far as CS and gold generation go and this win was largely due to a performance between the 2 teams then any 1 individual player playing super well. the three worst preforming players where all on Lucians team and despite this he did well in the desired metrics for an adc champion.
You mention that you went a kill for a kill after blowing flash, not exactly an outplay moment, getting him in a team fight with a single Q when he was low health is also not really representative of your skill as well. You should be bursting squishy so that's good and I'm happy your targeting the correct threats in fights, but its a collective effort after lane phase ends.
TLDR, Calling this guy out and claiming credit for beating him comes to me as disingenuous, especially when you provided inaccurate and unclear information on his CS and the match length. I hope in future posts you try to consider the impact of teammates a bit more for both sides and mention it. Alternately you may wanna start using the replay feature if you just wanna make a highlight reel post.