Shifting plumbing instead of hacking up the cabinet is definitely the lesser evil, though it’s not exactly fun wrestling with old copper lines or PVC in tight spaces.
Man, you’re not kidding about wrestling with old pipes. Last time I tried to nudge a drain line over just an inch, I ended up with a face full of ancient dust and a knuckle scrape for my trouble. I always get nervous messing with anything behind the wall—one wrong move and suddenly you’re patching drywall or, worse, calling in backup.
I’ve learned (the hard way) that MDF is basically a sponge in disguise. Even with all the silicone and sealers, if water finds a way in, it’s game over. I once watched a vanity base swell up like a loaf of bread after a slow leak went unnoticed for a week. Not pretty.
I do like your idea about vent holes for airflow, though. Never tried that, but it makes sense—anything to keep things dry. Still, I’m always double-checking for leaks before I call it done. Maybe I’m paranoid, but I’d rather spend an extra ten minutes now than deal with a soggy mess later.