I think stats are very useful, as long as you understand how to use them. Stats are necessarily based on past performance. This means that stats have limited predictive ability. For example, people often say a player will regress to the mean. That may be true of certain types of statistics, but it is incorrectly applied to player performance. An injury affects performance which affects statistics. This mean the statistics should reflect the physical condition of the player. It is the physical performance driving the statistics, and that always needs to be taken into account when looking at the numbers. Players don't regress just because regression is a statistical concept.
Some stats, like OPS are just bad stats. You shouldn't add together averages that have nothing to do with each other and that are calculated differently. And one of those averages, SLG, is a very flawed stat by itself. It assigns a value to each hit based only on the number of bases touched on the hit. Is that really the true measure of power hitting? Batting average is scoffed at, but that isn't because it assigns value to hits. It has the simple job of calculating the average of how many at bats produce a hit. And if that is all it is used for, it does a pretty good job of that one aspect of the game.
It is really all the statistical shortcuts that are the weakness of stats. Sabermetrics came along to improve that. But on this forum I would say that sabermetrics aren't really used, and I include myself.