It's true and I have the receipts.
The DC to cast is 10+spell level, so for a 1st level spell that's a default 50/50 if you get no bonuses.
But yes, you get to add your ability modifier. You get a +1 if you roll 12 on 3d6. That's a 12% chance of having +1. What about 14 on 3d6 - that's 7% chance to be +2. Those aren't great odds to balance a game system on.
You have advantage to cast Magic Missile - so better odds there. But Magic Missile isn't going to save your bacon.
After leveling up, you have a chance to get +1 to casting checks or advantage on casting a spell you pick, but even then the spellcasting isn't what I'd call reliable.