The Vanguard Australian Shares Index ETF (ASX: VAS) is a very popular exchange-traded fund (ETF) on the ASX, with an ETF size of $17.7 billion. It's the biggest ETF on the ASX.

However, being popular doesn't necessarily mean it's going to deliver big returns.

In the last five years, the VAS ETF has delivered an average return per year of 8.2%. That's not bad.

Compare that to the iShares S&P 500 ETF (ASX: IVV), which tracks 500 of the largest US companies. It has returned an average annual return of 16.3%.

What's the difference? The IVV ETF provides the most exposure to leading US growth shares, whereas the VAS ETF gives a lot of exposure to ASX bank shares and ASX mining shares. Those two sectors can perform well in a one-year time period, but they're not known for producing big returns over multiple years.

The ASX represents Australia

There are some internationally based businesses on the ASX, but the ASX share market largely represents the Australian economy.

A big portion of our economy relates to property and digging stuff out of the ground, so it's not surprising the index includes significant representation from those two sectors.

Look at the biggest companies in the VAS ETF and their market capitalisations, according to the ASX.

Commonwealth Bank of Australia (ASX: CBA) – $261 billion

BHP Group Ltd (ASX: BHP) – $201 billion

CSL Ltd (ASX: CSL) – $135 billion

National Australia Bank Ltd (ASX: NAB) – $114 billion

Westpac Banking Corp (ASX: WBC) – $110 billion

Macquarie Group Ltd (ASX: MQG) – $85.4 billion

ANZ Group Holdings Ltd (ASX: ANZ) – $85.2 billion

Wesfarmers Ltd (ASX: WES) – $83 billion

Wesfarmers has significant exposure to the Australian property market with its Bunnings business, which makes the lion's share of profit.

I'd say CSL, Macquarie, and Wesfarmers are the only ones on that list delivering solid long-term earnings growth and are likely to continue that trend.

Earnings growth is the key driver of the share prices of profit-making companies, in my view. I think that explains why the VAS ETF unit price has only risen 15% in five years – earnings growth by the big miners and banks hasn't been compelling.

ASX growth shares are becoming a bigger piece of the pie

Of course, there are some compelling ASX growth shares that are increasing earnings. They just haven't been a large slice of the pie (yet).

With how quickly some ASX growth shares are scaling, they are becoming a more influential part of the S&P/ASX 300 Index (ASX: XKO) – the index the VAS ETF tracks.

The bigger these ASX growth shares become, the closer the VAS ETF could be to being called a growth fund. It would also help if the market caps of ASX bank shares and ASX mining shares declined, though I'm not hoping for that.

Now, let's look at some of the largest fast-growing businesses and their market caps. I expect that (at least) one of the names below could eventually become larger than one of the major banks.

WiseTech Global Ltd (ASX: WTC) – $40 billion

REA Group Ltd (ASX: REA) – $34.4 billion

Pro Medicus Ltd (ASX: PME) – $26 billion

Xero Ltd (ASX: XRO) – $25.4 billion

Thanks to earnings growth and market capitalisation growth, these businesses are bigger than they were a year ago and much bigger than five years ago. I think this is a positive development for the ASX share market.

VAS ETF Foolish takeaway

The VAS ETF is an effective way to invest in the ASX share market, but I'm not expecting it to deliver as much capital growth as the global share market or individual ASX growth shares. That's why I'm looking for opportunities in those two areas.