After listening to a paul merriman debate on the merits of small cap investing, I compared returns over the last 25 years

I kept hearing that within the last 3 market cycles, that small cap has under performed.

So I compared the s&p 600 sc value index vs the s&p 500 and I plugged in various dates i.e., 2000-2021, 2000-2012, 2004-2021 2005-2025 etc..

And what i found was if you were invested in slyv which tracks the 600 value index. From anytime before 2004 and held to roughly 2021, you beat the s&p 500. But if you bought in after 2004, then small cap under performed the s&p 500.

After 2004, each subsequent year if you were to purchase both spy and slyv then spy out performs, especially starting around 2010. But from 2021 to today, large cap has trounced small cap

Anyways I guess what I'm trying to understand is, when people talk about how small cap has been under performing. Isn't that just dependent upon when you entered you entered? BecauseIf I bought 100 shares of slyv in the very early 2000s, I'm in a much better position then if I bought 100 shares of spy

It just seems like when evaluating past performance, it's highly dependent on specific dates. To get a accurate picture you would have to look at a bunch of dates rater then simply looking at a 1, 3, 5 year period