The tautological "correct" play is to only make moves which make your position better. Your formula makes some assumptions about what is "better," specifically that having fewer pieces on the board is better.
This is not always the case. Sometimes you might be trading an active and useful queen for a passive and entrapt queen, which stymes your attack. Such a trade is not useful. If you are on the attack, trading generally dilutes the attack. You want to get more for your trade -- you want to get a positional advantage as well.
However, the real challenge you will face in this situation is a circular logic that will form over time.
- At the point where my pawns and pieces are in a better shape than opponent's, I first exchange the queens.
What makes "pawns an pieces" be "in better shape than opponents?" That's an open question, and the subject of countless Chess books. You answer that question with 4 and 5:
- Centralise my king
- slowly exchange all the minor pieces, then the rooks.
By definition, being "in better shape" starts to become "in a shape such that centralizing the king and then exchanging pieces results in a win." And this is where you can get in trouble. You are less inclined to explore tactical situations where this 2 step formula does not result in a win. And, as others have pointed out, it will be hard to grow to learn these positions if you avoid them.
The failure for this formula will occur at the point where you face strong enough opponents such that they not only fight on the board, they fight in your mind. They aren't just looking for strong positions on the board, they are looking for positions that your mind is weak at.
How do you find these positions mid game? Your opponent would do this by looking at the sorts of moves you choose, and the sorts of moves you elect not to play. If they start to recognize that you, as a player, prefer positions where "centralizing your king and slowly exchanging pieces" wins, they won't give you those positions. Indeed, they'll start giving you bait: positions where centralizing your king and slowly exchanging pieces results in a loss but looks promising. Then, when you least expect it, they drive you into a "tactical" line that you weren't prepared for.
What you describe is a plan. Famously, as Former President Eisenhower put it, "plans are useless, but planning is indispensable." Its fine to start games with your formula in mind, but make sure you are not enslaved to that plan. That goes for the metagame too. You may never reach the point where you can beat a 1500 player 100% of the time before you learn tactics. Be ready to deviate from that plan when you realize that it is starting to handicap you.