Trend lines are without a doubt one of the most useful aspects of analysis but people often over complicate them. To say trend lines are useless is naive.

Once a HTF trend line is broken and the retest area makes sense then you have a clear area for price to move to where you can look for some entries.
Once the retest makes no sense (ie goes into a negative price) then you look for the accumulation structures instead of crashing structures. Here you would look for a less steep angle of descent on a trend line and find the medium timeframe trend break and retest.
The final stage would be an even flatter LTF angle of descent trend break and look for an Inverse H&S set up or Three wick pins for true bottoms to occur with a horrible looking candle to pinpoint a real bottom.
The annoying thing is when market makers push prices into zones to build the opposite trades, they have numerous techniques and algos to be able to take out traders in the final moments before true reversal. The algos will never be beaten and are a real money maker for the middle man of the markets.
But if you focus on solid assets that have survived many bear markets and increase your DCA method as the timeline of trend lines progress. Then by the time a bullish spike comes you will be in profit land before others can even have time to figure out what to do.
A very simple process to follow but it takes 4/5 years of waiting around sometimes before you finally get 3 months of crazy price action.