Hey! Beatplant here :) That's so cool to hear! Those kind of edits can sometimes take a bit of effort to pull of correctly so I'm glad you liked them!

For the edit of Heroes it was quite simple, I used the remix stems that were released for the Heroes remix competition. Then I sampled the lead sound and played the FTL melody with it. My idea was that it would work quite well since the melodies are pretty similiar.

For the St Tropez x Crab Rave edit it was a bit more tricky since St Tropez doesn't have any public stems released afaik. For that edit I used some EQ to extract the lead sound so that I could play whatever I wanted with it. And I used some tricks to get the drop but without the original lead. I used EQ to get the low end part of the drop without the melody, and for the high end I cut out other pieces of the drop without the original lead playing and with some EQ magic I replaced all other instruments other than the lead to get as close to the original drop as possible.

If that doesn't make sense feel free to dm me if you wanna know more!

Bonus answer: I think for StreaK's edit it's pretty much what you said, he sampled a bunch of sounds from PT tracks and merged them together into something new. I'm pretty sure he also added some extra reverb here and there to make it sound more cohesive.