Your tl;dr and the rest of your post don't line up. "The" meta has nothing to do with item builds, it's what champion's strengths best suit which environments (aka, top lanes who can defend themselves, or mid laners with burst or utility to give 2 examples).
Furthermore, this has little to do with a preconceived notion of what's right or wrong, as most claims towards champion builds are based off what is simply the most efficient. To put that into context, most main carries have nothing but Damage and Utility in their kit, for example
or
. There is literally no good argument for building these guys (overly) tanky, or else they'd fall off a cliff in terms of usefulness as their only main reason for being on a team, damage, is shot. Full AD and AP builds exist for these guys, along with hybrid and pseudo hybrid builds, but you can not argue that these guys not really being able to build tanky is the result of an oppressive community+riot holding down your creativity, that is just suboptimal play. AD Akali for example makes little sense in most contexts, as AD building on a champion with low AD ratios on abilities suggests that your damage will be in the form of Auto Attack based DPS. This is silly when you consider that both her Magic Damage DPS and her Magic Damage Burst is far higher thanks to her Q and her Ultimate's functions, along with being far more reliable with her W, compared to the fact that unlike most other melee carries, Akali has no way to defend herself while she's trying to auto attack away.
I mean, if you're going to argue with me that playing sub optimally should be celebrated by this community, go ahead, please do. Just please let my message get across that most arguments against building champions weird is all about optimizing a champion's strengths.
P.S. As an engage champ, Blitzcrank top, and in rare cases, Blitzcrank mid are actually perfectly viable provided you are either building the AP/Magic Pen to burst people down or the tankiness to be your team's main team fight initiator. The people who were criticizing you in that game were just idiots. However, if you built something like AD or Utility Blitzcrank while you're in top or midlane, then I'd say you're the one who messed up in that case, as building AD doesn't take advantage of Blitzcrank's engage power the same way AP or tankiness could, and building like a support while in a Solo lane will simply make Blitzcrank extremely useless through the laning phase.