Great idea to focus on improving one thing at a time.
That's a standard technique in most sports.

When you try to address too many points at the same time
you don't really develop much muscle memory.

You can always work the morning on one thing, afternoon on another,
then try and put them together during the last sessions.

And don't worry about your speed.
In the slow sessions, it's not the lapped riders that are doing anything wrong,
the faster riders are just riding in the wrong group.
(Plus, as long as I'm out there you'll never be the slowest rider.)