Honestly, in my opinion the Echo is one of the most difficult parts of the lore to define. In the end ARR sort of relegated it to be more of a plot device than an actual organic piece of lore and its frequency, potency, powers, and manner it can be altered vary wildly person-to-person as the plot demands.

In 1.0, the Echo allowed us to (arguably) physically appear and interact with the past instead of just getting a flashback with static. In a random cutscene with animation the likes of which we'll never see again (but with the most boring music imaginable), Y'shtola was able to alter our Echo back then in one instance when she kicked us out of the Echo and into the present right before a tsunami slammed into the ship. She was also able to jump into a different Echo "vision" we had, the feedback causing the WoL and Y'shtola to fly apart when it ended.

In case you want to see the cutscene I described: https://youtu.be/jyB1iuB-Bkw?si=sSZsWq-69T87DPYq&t=499