I will admit that it can be tricky to know for sure how much time you’re saving with improved emulation, and it really depends on the game in most cases.
One really simple way is to subtract the amount of lag frames in the game, this can be from taking the total lag frames and subtract it from the total frame count. However this may not always be accurate since some games may handle lag frames differently. A more consistent method would be by comparing each stage or area by their frame counts, and ignore loading areas. A good example from one of my submissions was the judgement from my Splatterhouse 2 submission last year:
http://tasvideos.org/6338S.html. Here, slamo created a chart that had a standard start time for each stage. This could be something like the first instance of movement from the character, or as soon as the screen fully fades in.
The other thing that can help is if you have a memory address that represents in game time, and it stays consistent even if the game has lag in it, that can usually be the best option to use as well. But that’s assuming the game you’re doing has that.
One thing I personally like to do is to import movies into the emulator I work with, and see if I can get it to sync and compare my wips with that. However I cant guarantee this to work every time since some games may have a varying amount of emulation differences, especially if RNG changes because of it.
So in general there are ways to compare movies that also removes emulation differences, and I’ll admit they aren’t always the most convenient to use. Personally I feel like I’m pretty experienced with movie comparisons in regards to emulation, so I’m used to it, but I understand why most people aren’t. If you are unsure if you’re saving time over an older movie because you aren’t sure if it’s just an emulation difference, there’s people on the site that are willing to help you figure it out.
Sorry for the wall of text, I just have alot to say about this topic.
EDIT: That being said, at the end of the day, Gens is still an accepted emulator. People are still free to use it if they wish. It's definitely not the worst emulator the site that's still being accepted, but that's also not saying very much. If you wish to use it, then that is your choice. People just generally don't like Gens due to how incredibly inaccurate and outdated it is.
