Hm, from what I can tell, watching the match overview as I write this.
Ekko gets first blood on a fuck-up by Yi. Yi later comes to gank around the time Blitzcrank likely lands a pull on their support Mundo, you teleport in to help the bot lane, Yi and the enemy Mundo feed. Later Lucian and Bliztcrank feed a kill to the enemy Vayne and Mundo bot, bot tower gets taken, Blitzcrank feeds another kill. Vayne roams to mid to help Anivia fight Ekko as Gragas comes to gank, Ekko and Gragas feed a kill. Lucian is trying to take bot, Yi comes to gank and dies because he's already behind and given up two kills, bot tower is taken. Yasuo feeds you a kill, Blitzcrank feeds Vayne another kill (beginning to see a pattern).
Already I can see that Blitzcrank is a liability of your team, likely not landing his hooks, and seeing he went Relic instead of Ancient Coin is already an issue considering those pulls are very mana-costly in the early game and doesn't let him get the speed boost from Talisman (since often bad Blitzcranks need that second speed boost if they can't make plays with their innate one or they fuck up somehow).
Ekko kills Mundo, then Ekko and Blitzcrank later feed their Mundo and Anivia a kill. Blitzcrank feeds yet another kill to Anivia and another of your towers gets taken (likely mid if I guess right). Then the first major and massive teamfight ensues favoring you: Ekko and Lucian feed them kills, everyone other than their Mundo feeds your team kills. This is the point where the small lead the enemy team had fell, and was your time to capitalize, and while their Mundo feeds a kill to your Gragas, Blitzcrank feeds yet another kill to Vayne.
The point where blue starts to get ahead is when dragon is taken and Gragas dies trying to get the dragon, from there it's another death by Blitzcrank and two towers taken under you. Then your next major breakthrough: you take a tower and get a kill off everyone other than Vayne and Anivia, although Lucian and Gragas feed another kill to Anivia. You then take another tower and take down Vayne but Lucian dies to Vayne in the conflict. By this point Blitzcrank is a joke and Lucian is beginning to seriously become a problem, and Gragas isn't looking too good either.
Case and point, Anivia and Yasuo get three kills from Gragas, Blitzcrank, and Lucian. Then you get a kill off of Yasuo, but Yi takes dragon even though their Mundo feeds a kill to Lucian somehow. So far, you haven't died yet and Ekko hasn't been a complete liability. Next major teamfight goes to your favor: everyone other than Anivia dies on their team and only Blitzcrank and Gragas die, Ekko is pulling his weight and Lucian is beginning to get out of his rut... until he encounters a hiccup and dies to Anivia, and one of their towers falls (I will assume top since there wasn't much activity in the top lane).
Next teamfight: Blitzcrank feeds, everyone other than Anivia on their team feeds a kill. Then Bliztcrank and Lucian manage to get three kills from Yasuo, Yi, and Vayne. At this point Yi is flailing, Yasuo either feeds or makes almost no impact, and Vayne just can't do enough. Another tower is taken, and a two for two trade of kills between Anivia and Yi for Gragas and Lucian, very good because without Anivia they lose a lot of power. Yasuo finally comes out of his shell and gets a kill from Ekko and Blitzcrank, although Ekko manages to get the better of Mundo and kills him before then.
So now your team has finally made headway, you are ahead, if things go your way you will win by simple attrition if the rate of kills for deaths goes the same. But things go horribly wrong in the dragon pit, Anivia is up and between her and Vayne they get the dragon and everyone other than you and Ekko feed a kill (Ekko still manages to at least kill Yi before you two likely high tail it out of there). Yasuo feeds you another kill, then shit gets real: while you manage to kill everyone other than Yi and Yasuo, it comes at a cost: Gragas not only feeds a kill to Yi, but Yi manages to take two of your towers.
From here it's downhill, Yi and Yasuo apparently get out of their funk, and while skirmishes here and there go either way (the next major teamfight is a three for three trade), what killed your team halfway between 39 and 40 minutes: everyone other than you dies on your team, and from there another dragon is taken, and by this point it's basically a slow death as two towers are taken, no major teamfights end in your favor, and Mundo isn't a champion you can duel an entire team with. All in all, I'd say that you did your best, nobody is going to fault you considering you only died at the very end, and Ekko flaming probably didn't help anyone.