Quite the opposite in fact… I find using the ESP-01 as a shield is every bit as stable, and a cheap way to add WiFi to an Arduino MEGA for the I/O win, or existing UNO projects that are already wired and working with 5v sensors, etc. (Like adding a motorized kit to a bicycle 
)
But I wouldn’t ever try to do the same “Use as shield” thing with a NodeMCU or Wemos, as they are already full dev boards.