Here's my counter-argument in case you were serious.
Dimwit #1: 555's fail when hell freezes over. An engineering intern can make changes and see it work. The PCB will cost more than the electronics. 555 as a component will be available for years.
Dimwit #2: Arduino/ATMEGA are so well documented that the next engineer supporting this should have no problem making appropriate changes even 10 years from now, assuming Microchip sustains the ATMEGA product line.
Senior Software Developer: You've introduced an attack vector [the web interface], increased the BOM cost [the Linux board], programmed it in a language that changes on a yearly basis [node.js]. Not to mention having to provide a Linux image source programmable [preferably eMMC], and ensuring compatibility of the web config for major browsers for the lifetime of the product. All for a blinking LED.