There are "similar pairs" of openings that really do play the same, and in some cases, can even transpose.
You are correct in stating that similar openings and similar pawn structures are NOT the same thing. As you mentioned, the Pirc and King's Indian are like Cottage Cheese and Chocolate Layer Cake.
That said, here's how I pair up openings and why (in d4/e4 format):
King's Indian Defense / French Defense - Both very frequently feature a completely blocked center, and both require the same strategy. Attack in the direction that the pawns point when the center is blocked. That means you should be attacking Kingside in the King's Indian lines where the center is Blocked and Queenside in French lines where the center is blocked.
Nimzo-Indian Defense / Caro-Kann Defense - Both usually involve a very fluid pawn center while at the same time, certain lines can lead to a blocked position (i.e. Leningrad Nimzo-Indian, Advance Caro-Kann). A frequent occurrence is to go up against the Isolated Queen Pawn, a frequent affair in the "main lines" of the NID and the Panov-Botvinnik Attack, in both cases White having the IQP, hence why you have to be good at going AGAINST the IQP, not handling it yourself.
Queen's Gambit Declined / Closed Ruy Lopez - Both lead to closed though not completely blocked positions with understanding of long term strategy and planning with a keene eye for tactical opportunities is critical, not memorizing reams of lines 20 to 30 moves deep.
Grunfeld / 2...d6 Sicilians - Highly theoretical, many positions that would be "confusing" to most that haven't specifically studied the theory, very aggressive in nature, high risk/high reward, lower draw ratio. Willingness to sacrifice the exchange, and knowing when to do it, is critical at succeeding in executing these defenses.
Modern Defense - Averbakh / Modern Defense vs e4 - The resulting positions are vastly different, but both involve having a keen eye for when to make the transition from slow, patient manouvering to when you jump out and attack. A clear understanding of weaknesses are in order here. Often times, it's about being very strong on one color complex, and weak on the other. Control of squares in front of backwards pawns, like if White plays c4, d4, e4, and eventually d5, controlling c5 and e5 is paramount, along with the dark squares in general. White has to rely on an attack on the light squares. If White gets in e5 successfully without self-capulation, White's probably winning. If he pushes e5, then d5 needs to be prevented with domination by Black of the Light Squares. So Flexibility is also in order for this opening.
Modern Benoni / Alekhine's Defense - Both are hypermodern defenses that allow White a huge amount of space. Black banks on White's over-extenstion, and often has to defend religiously. But if he can get out of it alive, White is often loaded with weaknesses if it hits an endgame.
Slav / Petroff - Both require deep strategic thought. Both are very solid lines for Black, but not as dry as say, the QGD Orthodox, Berlin Defense, etc. There is an ounce of poison in these openings, and knowing theory can be critical. One slip up can often mean death despite it looking like nothing is really happening. Early Endgames are also prevalent in both openings.
Does one guarantee the exact same play will occur every game listed in every pair? Of course not! Many of your Frenches will play out very differently than your King's Indians, but from the 5000 foot level, the two are very similar in nature in that they require a similar train of thought to succeed. They both entail attacking the side the pawns point to, whether that be Kingside or Queenside.
As for White, it's harder to get similar play to your Black game. Playing White requires a more diverse knowledge of openings, but it's not like you have to know any one opening in its entirety. If you play 3.Nc3 against the French, there is no reason why you need to know about Advance French or Tarrasch French. As Black, you need to know all lines of the French, but then there's no need to know anything about the Sicilian, Latvian, etc. As White, while you may be able to get by on just one variation of the French, you also need a line against the Caro-Kann, 1...e5, Pirc, Modern, Alekhine, etc.
Hope this helps.
Hey everyone,
I'm 18 years, play chess for 5 years, around 1.900 Elo and want to improve. Openings aren't the first thing to train, but I want to settle for a repertoire to play for a long time now.
The only mainstay in my repertoire is the Caro-Kann (began with Open Games and had some escapades with French and Sicilian thought). Against 1.d4 and with White I don't have a repertoire and swich a lot. I like the NI/QI-combo, but don't want to spend a lot of time working out special variations against 1.Nf3 or 1.c4, that's why I abandoned them. I think the KID (which I played a lot, too) or a Slav variation (c6-d5-setups are move-order-killers) are just more practical. Here are my general questions:
1.) To what degree does a repertoire has to be "coherent" and does this even matter? I naturally want to play "opening pairs", say KID with the French or Breyer Lopez (I don't think Pirc or Modern are similar to KID just because the first moves are the same) and Classical Slav with a Caro-Kann. Is this nonsense or normal? There are some other thoughts, too: Is it better for chess development to play openings, which complement each other and gain a deep understanding of the arising structures, or should I play openings that differ from each other to widen my horizon?
2.) I always paid more attention to Black's openings than White's and I become increasingly uncomfortable playing the white pieces (and that's not a good sign!). I cannot target it concretely, but it just feels for me like White has no real "interesting" ways to play, like I cannot find variations that please me. Discussing this with some strong club members I always get to hear: "This is nonsense. White can/should play for the advantage and has so many ways in doing so, so just choose one.", but this doesn't really help me. Does someone have similar experiences (maybe reversed) and can help me: Is this a psychological problem playing White or just a lack of knowledge in openings?
3.) Regarding questions 1.) and 2.), how could a White repertoire for an ambitious Caro-Kann & Slav player or a KID & French player look like? (Of course no concrete lines, just hints and directions, what to look for...)
Thanks and best regards!