In a 5g filtered/cycled and planted with one Betta, IMO-water changes of 50% weekly, however, depending on the number and type of plants the percent could be less and vacuuming weekly in areas without plants with a light hover in areas with plant roots so not to disturb the roots.
You also have to look at the fish waste as ferts for the plants and by leaving it the plants eat good...but, depending on the number/type of plants too much waste can cause too high nutrients and then algae or ammonia.......
Hard to give a straight answer when you can have so many variable and this is often why you can have so many different answers to the same question....you have to find out what works best for your tank, fish, source water...etc......laffs....wish it was that easy...but a good starting point IMO would be weekly 50% and as you go and test the water tweek-it to fit the tank/fish/plant needs...everyone of my tanks has a different cleaning level, time, percent all based on the tank itself
Fresh, clean, dechlorinated water can be a good thing and it can also prevent health and fin issues, even when the water look clean and clear you can still have organic that need to be removed, however, lots of the right type of plants can work as the filter decreasing the percent need of the weekly water changes.
You can baffle the filter if it seems to be too strong, however, as long as the Betta can get away from the current to rest, IMO the current can be a good thing and help exercise the Betta...but on the flip side-that same current can shred fins........like a flag blowing in the wind......
What kind of plants and how many plants, what kind of substrate, type of lighting, watts per gallon, ferts used, feeding schedule, photoperiod, age of set-up, stocking, filtration type..... etc are all factors that can play a role in how much and how often the water changes need to be IMO/E