I haven't seen one problem at all with any puzzles up to the 2700 level. Some problems will be harder than others and that's simply just some motifs your familiar with and others you aren't. I've used chesstempo,
chess.com, and lichess in my opinion has the most realistic problems that correlate to a real blitz or rapid game. I'll use chesstempo for practicing longer combinations and vision but lichess for purposes of blitz and rapid is hands down the best puzzles.