Some systems see their greatest success early in their generation, and some are "late bloomers".
We saw this during the last generation (Wii, Xbox 360, and PS3). This generation started in 2005 and is coming to an end. I'll call the core generation 2006-2014. This was the period where all three consoles were on the market.
The Wii was the ultimate "early bloomer" - it peaked early in that 2006-2014 timeframe. Around 2006-2009, the Wii was selling like hotcakes, with an abundance of third party support. The Wii began to lose momentum at the middle of the generation, with sales slowing by 2010. The last year the Wii moved any significant number of consoles was 2011; after that year the Wii was largely dead, superceded by the Wii U in 2012. So the Wii was wildly successful the first 3 years, still successful in the middle 2 years, and virtually dead by the last 2 years.
The Xbox 360 enjoyed strong sales throughout the generation, although it lagged behind the Wii early on. I'd call the 360 a "balanced" console, pretty well peaking at the middle of its generation and strong throughout its generation, living to see the finish.
The PS3 was the "late bloomer" - it sold relatively slowly through the 2006-2008 period, due to high price and smaller game library than the 360, while having to contend with the novelty of the Wii. Around 2009, with the game library picking up and lower prices, the PS3 gained momentum, and hit its peak in 2010-2013. Maligned at launch, the PS3 went on to be a very successful console as well.
The previous generation (circa 2001-2007) was pretty well dominated by the PS2. The generation prior to that (circa 1996-2001) was dominated by the PS1, although the N64 was stiff competition during the earlier parts of the generation, but declined after 1999.
The 16-bit generation provides us with a perfect example of a system war without a clear winner, but the early part had a winner and the late part was won by the other console. In this case, Sega won the early part and Nintendo won the later part. The 16-bit generation's "main part" was from 1991-1996. At the beginning of this period, Sega's Genesis was very strong, bolstered by the launch of Sonic. The Genesis also had far more games than the SNES early on (1991-1993). It wasn't until about 1993 that the SNES had a game library that could compete with the Genesis. But around 1994, the Genesis began to lose momentum (thanks in large part to Sega doing stupid shit) and a lot of the SNES best games came out in 1994. So 1994-1996 belonged to the SNES.
It seems that the systems sold on novelty win early on, and the ones that have the best game libraries peak later.