Historically, a 70/20/10 would grow more than 5% most of the time. Bad years would be obvious exceptions. 2017 was a great year for markets. If you are using Vanguard index funds in that allocation you should have seen more than 5% growth in 2017.
How are you measuring growth? You mentioned capital gains and dividends. Are you referring to your capital gain distributions on a tax page? If so, that information is for tax purposes. Your performance is likely different. Tax efficient stock index funds, like Vanguard's, don't distribute capital gains most of the time. They keep the gains inside the fund, and you will likely only realize your gains when you sell the investment in the future. This is great, it defers when you have to pay taxes. If you want to see how your investments performed go to the personal performance page on the Vanguard website. That will give you actual performance information.
If the lower returns are showing even on the personal performance page then please let us know what you are invested in because that is out of the ordinary.
The future is unknown. A 70/20/10 has historically grown more than 5% per year, but there were whole decades where it averaged less. This is why the 4% rule is so popular, because it takes into account the ups and downs of the market.