three big factors:
you lacked a proepr comp for synergies, only two small buffs(2nkight, 2gunslinger)
Most of your oieces were low tier(1 and 2 goldcosts)
Your lacked a proper hardcarry in terms of items(unless the other item on tris was IE)
Luden's on lucian is nice early, but not that impactfull later on, on kennen it's a bit better but still not as impactfull, and rageblade without any ad or on-hit isn't enough on tris.
And the items on garen are kinda wasted, he gets nearly no use from the AD as his base AS sucks and his skill prevents him from AAing for quite some time, and him haveing zekes most likely means the 'aura' buff is applied to the frontline rather than your backline.
Later on in the game, teamcomposition is very important, and higher tier units at silver can easily keep up with low tier on gold. A silver Seju is stronger than a gold Garen for example, she'll be just as tanky with a more impactfull skill.
Also, haveing the right combination of items on the right pices can make a big difference. A silver tristana with rageblade, shive and IE will deal alot more damage than a gold tristana with only rageblade, especially if you get the full 4 gunslinger buff ontop.