I had some VASGX for a while but not any more. That's because it didn't suit my changing needs; it might be fine for an investor whose needs it serves more precisely. At the time I wanted something that would automatically balance several things at once - bonds vs stock, international vs US - and it did that.
I wouldn't judge it based on just the growth rate. Investments take a very long time before that can be an informative comparison, because in short periods like 1 to 10 years (grin), temporary conditions give one investment type a temporary advantage over another. Also different investment types should have different growth rates because they have different risk levels. For example, last year a fund of tech stocks would have a far superior growth rate; this year, one of the highest rates of loss. Such a fund is riskier in the sense of being more volatile that VASGX, but whether its growth is more or less depends mostly on what period of time you measure.
VASGX has a bond component. In the long term, stocks produce higher returns most of the time, so if you're 20something, growth over time by an all-stock fund will probably be better. That, not the growth rate of some recent period, is a reason for picking one fund type over another. Invest by finding an investment that suits your investing needs.
In comparing VASGX vs an S&P 500 fund, another difference is that S&P 500 is all US companies, VASGX includes international ones. Which is better depends on future trends, which of course are hard to predict, and whether there are sustainable differences between US and international companies' stock markets. I used to assume that international markets would trend over time to the same result as US ones, so that diversifying would automatically buy cheap companies that would later reach the same price as US ones; VASGX is a good way to invest in this belief, if the belief is true. Later I began to realize that some differences between countries might produce permanent differences in results and maybe the foreign stocks woudn't catch up, meaning that VASGX would mean systematically investing in weaker stocks again and again, a waste of money. I acted on my new belief by selling VASGX but maybe time will prove me wrong. It's hard to know whether the international component is actually better or worse for you, I'm just mentioning things to think about. Sorry not to have a clear answer on that one, but sometimes a clear answer just means ignoring things that make a difference.
I'd at least switch to buying S&P fund for new purchases, on general principle. Also because a fixed monthly purchase buys more shares when prices are cheap.
I hesitate to say dump VASGX for an all stock fund because I'm personally going through my first phase of maybe market timing, and am kind of nervous about stock prices AND bond prices. Full disclosure - I danced out of the market earlier this year, got back in at a discount (success! temporarily at least), and now am considering ducking at least partly back out. If my worries are correct your best tactic might be sell VASGX, then stay in cash until the market finishes crashing, then buy your stock fund(s). Historically this is considered a poor strategy, but it's why I hesitate to go full S&P right now. This paragraph expresses personal opinion, definitely not standard investing wisdom.
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If you're going to stay fully invested, and take a long term approach, you might consider a fund that includes small cap stocks, not just an S&P fund. Sometimes small stocks perform much better than large ones. Historically over really long periods, the small stock advantage has been pretty strong, especially for small cap value. No one knows whether that will be true in future but there's a decent chance your returns will eventually be better that way. For example, instead of VOO (Vanguard S&P 500 ETF) you could buy VTWO (Vanguard Russell 2000 ETF). Or half VOO, half VTWO, and rebalance annually.
https://money.usnews.com/funds/etfs/small-blend/vanguard-russell-2000-etf/vtwo
