The trails are the same. The difference in disipation is a matter of atmospheric conditions. If the upper air is still, especially if it’s under a pressure system, the trail will maintain shape for a long time; if the upper air is mobile (has a breeze) they’ll disipate quickly. It’s just like any other cloud, the less it’s stirred the more it stays.
I've lived in an area with heavy jet traffic overhead, passenger, cargo and military, for all my life. There is a difference. You can see the two side by side, simultaneously. I'll have to disagree with you, they're not the same. As far as any nefarious intent or supposed health threat, I don't subscribe to that. But, they're there.
Such an obvious point, but lost on many. Most people probably think the atmosphere at 35000ft is pretty much the same as the atmosphere outside their front door.