I am always very sceptical when people try to tell us the markets have changed. The markets don't change, only price changes. If a strategy worked on pure TA 10 years ago it will work now. I try to always challenge these guys to show on the chart what has changed and they can't do it.
However, as I said above, one thing that does change which is not easily apparent from the charts is volatility. This doesn't show so well because the software we all trust to show us charts adjusts the screen scale so that the price action fills the whole screen space. This makes comparing volatility over different periods difficult. e.g. see the Dow for 2005. My chart shows all the price action confined within 1,000pts on the Dow, from 10,000 to 11,000, so about 10% of the starting value of the index. Then look at 2016: chart runs form about 15,400 to about 20,200, or about 30% of the starting value. But the two charts are the same size. So a strategy that works in low volatility time like 2005 might be wildly risky in a year like 2016: likewise a strategy that works in high volatility times could struggle to break even in ranging periods..
This is despite the obvious fact that some strategies are designed to work in break-outs and some to follow trends. Both these characteristics occurred in both periods but the volatility is the differing factor, not trendiness v's ranginess.
This scaling issue also means you can never trust the angle of slope of a trendline or MA. Obviously, up is always up and down is always down, but I have seen some strategies that demand a steeper slope of one or the other to work - and this is a nonsense rule built on quicksand which will fail.
Best of luck.