Hey Samudra,
I was in Medewi 2 weeks ago and had an absolute blast. Stayed at the Bombora lodge that overlooks the point and it was all good.
I think we maxed out at about 35 odd in the water mid morning and yes there are plenty of learners getting pushed in by their local coaches. In saying that I thought they were pretty good at letting a few waves go through or calling off the learners when someone else was on but of course it doesn't work all the time. I was up and out at sunrise and the learners really didn't start showing up till about 8 so there is a good couple of hours for the early risers where it is fairly quiet. The schools were only out till about 10 and the real learners did stick right on the inside and out of they way for the most part... You have to remember these guys are earning a living off the surf coaching (and photos and tee shirts) in an area where there is buggar all else to do so I was happy to work in with that.
We had some good swell at around 4ft and the wave is just magic early with the offshore wind... I am a filthy SUP rider but it wasn't too hard to stay out of the way and pick up plenty of good waves. The break really suits longboards up to the size we had... nice and mellow with a couple of steeper sections similar to Caangu But there were plenty of short boarders ripping it up. Would like to see how it works when it is a bit bigger. There are quite a few other breaks in the area that are nowhere near as crowded as the main break as well.
Talking to the locals, Jun/Jul the place is pretty mad and they do get big crowds... personally I would steer clear at that time of the year but Medewi will stay on my off season list. I would imaging during the rainy season the water would be pretty ordinary though as there are a lot of rivers out of the mountains in that area but I reckon the water was cleaner than Legian while we were there though....
Best bet... talk to the locals so they know you aren't just a breeze in (it is their back yard after all), buy some tee shirts to support the local board riders and some photos off the boys.... and get in at the crack of dawn when the conditions are at their best. Gives you time for a second sesh after all the learners have buggered off!