first off, your example from fighting games is a bit flawed. i'm not experienced in that genre so i can't give a comparative example, but to be blunt about it, most pokemon suck so much that they will never be able to cut it in OU. you could certainly build an OU team focusing entirely around articuno, and if you were a great teambuilder the team would work. however chances are you'd find articuno did relatively little in your battles, and it would rapidly become the weakest link. synergy is a crucial concept in pokemon team building yes, but it has to go both ways. weak mons contribute so little to a team that they become little more than a load that the rest of the team has to carry. your example would be better suited to an environment like a double battle, where two pokemon can directly support one another - that doesn't really happen in singles pokemon besides mechanics like wish or baton pass. synergy in singles teams is higher-level than that; it involves looking at a team as a whole, analyzing what beats you and what you beat, etc.
the thing to understand about lower-tiered mons is that every mon that's used in OU has a niche, somewhere. if we look at cofagrigus for example, it's just another ghost with willowisp and pain split, but what it has going for it are superb defenses (compared to other ghosts; generally a frail typing stats-wise) and haze. these things are really not all that good considering cofagrigus's many other flaws... but in OU, they're just enough to give it a place. if that niche is precisely what your team requires, fly with it! but to build a team around a mon so weak is generally flawed from the start, and it's crucial to understand that a mon falls into a lower tier because its niche in higher tiers is too small to justify wide spread usage - hence, it's harder to make use of a lower tiered mon. i'm one to talk seeing as my preferred playstyle is weatherless stall, but don't be too hipster about it - trying to build a team of inferior mons just to show the world who's boss is going to obviously end with an inferior team, lol.
as for your team building issues, you have the inevitable problem that one encounters when jumping into any competitive game, which is concept overload. as a game becomes played more and more, gameplay becomes distilled and stratified, and the things that distinguish components of the game from each other become more and more advanced. high level play is all about grasping those concepts and using them to your advantage.
that paragraph of fancy talk garbage was basically a long way of saying "team building is difficult and there's a lot of shit to account for". hence my recommendation would be to go and read the analyses for the pokemon in question. you're getting hung up on a certain factor in pokemon, in your case BST. base stats are important, yes, but certainly not the end-all - otherwise explain how kyurem, a 660 BST monster and a dragon type to boot, doesn't even get enough usage to be OU.
learning to team build is a difficult process, and everyone learns it differently. there are a million ways to run a pokemon team - there's an entire spectrum between offense and stall, and you can incorporate all sorts of other modifiers besides, such as weather or even full trick room. i learned by reading a lot, lurking a lot, and waiting a long long time (i actually only started laddering seriously within the past two weeks but i've been on smogon for four years). there is no easy way out; you'll have to experiment and learn what works for you.
finally, don't double post, you can edit your previous posts by clicking the edit button on the lower right of each post.