I’m not sure if anyone already suggested this.
I’d like to suggest Insert blank keyframes(vector layer) in the timeline similar to Adobe Animate’s
as a way of
#1 minimizing the number of layers you need to get the job done, which in a way also improves performance
#2 as another alternative of doing frame by frame animation (aside from switch layers),
so that when people asked if Synfig is good for frame-by-frame, then we could say it is just as good for frame-by-frame with the advantage of being able to
#3 simultaneously do frame-by-frame and shape tweening(via spline tool)
The source:
https://helpx.adobe.com/animate/using/frames-keyframes.html
Hi and welcome here 
Synfig and Adobe Animate don’t share the same philosophy about keyframes.
In Synfig, a keyframe affects all the values of the whole animation (=all the parameters for all the layers).
Intermediates steps, where each parameter of each layer can change its value independently is a waypoint.
You can add any keyframe you want, but everything will be initialized with a set of values.
You can move a keyframe, but be aware that all the waypoints between 2 keyframes are placed in relative way, they will expand or compress.
And Synfig in nature is not made for frame-by-frame 
Oh, I see. I guess switch layer is the best way to go for emulating frame by frame…
By the way, thanks for giving us a wonderful program to use. I really appreciate it.
I’m excitedly anticipating the v2.0 release even when I know that it’s going to take awhile.