It may be worth running it for a while on premium fuel, and/or trying a fuel additive carb/ injector cleaner, Forte and Marvel Mystery Oil get good reviews. It might not work but it beats stripping the carbs if you can avoid it, Good luck.
Get some carb/injector cleaner additive for petrol engines and give the fuel tank a double dose of the stuff, if it says add 50ml per 5Ltrs shove in 100ml. There is a very good chance that it will clear it out, if it does not do it again with the next petrol fill up as the stuff sometimes take a while to remove built up varnish in carbs.
If it does not do it it will have only cost you the price of the additive if it does do it you have been saved a lot of hassle and you have still been riding your Yammy.
Win win if it works, if it does not work the rest of the fuel system will have had a spring clean fuel pump and lines.
What you describe would indicate a partially blocked jet or jets, especially as you ride through the flat spot and the bike surges forward again on to full boil, so it not an blocked air filter, as it would get worse not better as you continued to full throttle the same can be said for a fuel filter, as it runs fine at low and high revs it can only really be a partially blocked jet.
I could just be just one carb that is messing about, a flat spot at those revs is much the same as a bike only running on three cylinders, and that effectively dead cylinder is putting a brake or load on the other three, so in real terms your are running pretty much on half power as you go through that flat spot, no wonder it feels like it takes off once past that flat spot.
https://www.ebay.co.uk/itm/1-x-WYNNS-PETROL-INJECTOR-CLEANER-ADDITIVE-325ML-ALL-PETROL-ENGINES-AND-CARS/131898749933?hash=item1eb5c733ed:g:k2MAAOSwARZXo1yNWynns is a reputable make and also the link above is a good price, sending off for a bottle myself just to run through my system.