Does it take more commitment to continue improving as your become better dancer? Let's say that for beginner dancing once a week allows very slow improvement. Would this change as dancer becomes better? Would the same person improve faster or slower when he/she becomes intermediate and still continues to dance once a week on average?
Depends on your goals ; What and how much you have to work on to get where you want.
In the beginning you are only working on a few things; like basics, timing, fundamental moves and leading/following to get social dancing. So progress seems relatively quick.
Often as you improve your eyes are opened to many more possibilities of aspects of dance to work on.
Then depends how good your fundamentals are. If you have to go back and fix a lot of things in order to make the next step. To clean up your technique.
It's hard to work on multiple aspects at a time. The more your focus is split the more work or time it takes ; If you want to work on connection, musicality, styling, body movement, improvisation... this takes time and dedicated focus on each aspect. Especially to improve the quality of what you do rather than just learning new things.
You also need to have a good teacher or guide who can show you the way and the opportunity to apply what you have learned. Much time is waisted with trial-and-error ; you need practice partners and a scene which is conducive to improving in that aspect. It would be harder to learn musicality in a scene with no musical dancers.
1 class a week for a year in a big city like London, LA or NY (ideally with social dancing 3 hours for each class) would more likely produce a better dancer than 1 class a week in the sticks, because with better quality partners you would learn much on the dance floor but some individuals could buck the trend. Especially if you only go to classes and hardly ever social dance.
It would also depend on your natural ability with your body, previous experience with dance in general, how good you are at picking things up and personal dedication.
If you are the kind of person who thinks how best to use that 1 hour a week. If you can do some complementary homework between classes like listening to Salsa, watching videos, practicing the basic (or what you learned in class) for 10 mins a day, it will reinforce and significantly reduce the time to apply it next time. Or you just go along and expect others to do it for you then go home and forget about it until next week.
During partnerwork classes your personal focus could be on the pattern, the technique, quality of basics steps, feeling and moving with the music, connection with your partner, improving body control.. many different things that may not explicitly be the focus of the teaching.
What happens when you are the better dancer on the scene. Who can you improve with if you always have to dance down? You have to find ways around this without alienating your current partners.
Travelling to another scene (or congress) with better dancers may help you get ideas where you should be spending your effort.