Since 2014 Roland Garros, #1 Novak Djokovic and #2 Roger Federer separated themselves from the field in terms of consistent top results. Some may argue that more recently, Novak Djokovic is the big 1 and has separated himself from the field, but this thread is not about that, so it is not up for discussion.
The chart above is the union of all the tournaments each of these players played in the period. A for Absences are the equivalent of did not play. O is for Other results than the getting to business end of the tournament (semifinals or better).
Their results since RG 2014 have been amazing for different reasons, and somewhat similar and complimentary. Novak holds the class edge, winning more of the biggest tournaments, but Roger perhaps surprisingly, has had more titles + runner-ups, and generally did better in the lesser tournaments. With the notable exception of Wimbledon, Federer generally did better in faster conditions, Djokovic in the slower, which is well known and accepted by most pundits.
Nobody else is close to these players in consistency and results in the stated period. Check it if you want.
Curiously, Federer stated before this year started that one of his goals for 2015 was to do better in finals than he did last year, where he made 11 finals (the most since 2007's 12: 8-4), but won only 50%, winning 5, losing 5, and did not play 1 (WTF). This year so far, he has made 4 finals and won 3. So far, he is meeting his goal for 2015. And in this stated time span, he is remarkably 8 and 4 in finals (inc. DC).
Djokovic made 8 finals last year, winning 7. This year, he has so far continued or even increased that pace and made 5 finals, winning 4. In the stated time period, he is 8 and 1 in finals.
Can we blame this period of dominance on anyone? Did these two take advantage of below par/injured-absent players like Nadal, Murray, Del Potro?
Do you see this trend continuing for the rest of 2015, or do you expect someone to invade their space? If so, who? Murray, Nishikori, Nadal? Will any of the younger guys step it up? Or will they continue to hit the wall?
Do you think Federer, now 3/4th of the way into his 34th year, will finally fall as the renowned prophet Everko prophesied, or perhaps even the mighty Djokovic will cool off?
Who knows, eh? In the meantime, enjoy the ride, and we'll watch and find out.