First of all, it’s a common misconception that high level players are always more skilled. Plenty of lvl 100’s reached their skill cap long ago, and still have no idea what they are doing. Others grinded all their levels in other game modes, which means they might be gods at Tank RB, but suck hard at anything related to planes.
There are also actually skilled players who play at lower BR’s, and there are multiple reasons for why they do this. Some are starting new tech trees or branches to unlock higher ranks. Some have a particular BR bracket where their favourite vehicles are, or where they think combat is most engaging. Some have introduced a friend to the game recently, and is playing together with them at their BR bracket. Others are farming SL or just straight up taking a break from higher tiers (seriously, anyone who plays 10.0+ br games for prolonged periods looses their minds. It’s absolutely mind numbing).
At last we have the actual sealclubbers, who have 2k games in their P-39N or equivalent. They exist, and there is a few of them, but it’s not a given that, even after so many games in the same vehicle, they actually know what they are doing. Some ppl get a kick out of dookie dumping on new players, and I doubt we can get rid of it. Clubbing exists in multiple BR brackets, and every time the Devs drops a new mean machine at a br way too low, we see these types flocking to it.
I’d advise to see these ppl as challenges instead of obstacles. It might sound a bit harsh, but once you learn to deal with them, you will probably have moved beyond their skill levels.