There are plenty of ways to see whether a trend is losing strength just based on the price action only - using no indicators.
First off - in regards to the question as to whether a pin bar is lagging, to some extent yes it is.
Yes because the pin bar by itself is a reaction to a price level and sellers rejecting price at a particular level. Thus, the pin bar is the result of the order flow - not the cause. Because of this - a pin bar is to many extents lagging because the order flow came in at the top/bottom of the pin bar, and those chasing to get the next best price created the wick of the pin bar.
Now as to how you can determine if a trend is losing strength, there are almost invariably two signs from a price action perspective a trend is losing strength. They are;
1) a greater/increasing presence of counter-trend players
2) an exhaustion/climax type move
For the first example - you will see this as a trend that was highly imbalanced, but then started to produce greater counter-trend swings. If the swings continue to increase and you see less price spreads, then its almost always showing a weakening of the trend by the very fact the counter-trend players are coming in with greater presence via the price action.
For the second example, all you have to do is spot exhaustion or climax price action, which is the result of the last traders chasing the market higher, along with the institutions giving it one last push to trap late traders in, thus fueling the counter-trend move after they exit and look to reverse (well - that's part of it as there is more, but describes the gist).
So the answer to your question is - identifying trend transitions /losing strength is quite easy to identify when you learn to read the price action well.
There is a ton more I could say on this for pages on end, but hopefully this helps give you some ideas. I actually wrote a large article discussing this at length called 'How To Trade Trends in Forex - What You've Been Missing' which gives plenty of examples, along with talking about the order flow behind these trend transitions discussing this topic and elaborating on it further - so feel free to check it out should you wish.
Hope this helps for now - but a good discussion indeed and a critical topic for trading price action.