HARD disagree, sure a little bit of Zro is nice I guess, (+100 a month from zro max, or I guess you can trade it? still not that great...) -10% empire size from pops is NOT worth a precursor race, and scientist experience is useless (it's really not that hard to get leader exp growth boosts).Zroni also give you...
...a lot of guaranteed Scientist Experience through their many, relatively easy digsites
...an above average amount of Minor Artifacts for a Precursor
...a few Zro deposits on habitable planets (which will be added to your income once colonized, even if you don't have the tech)
...Psionics as a tech option (and 25% free progress on it - only if you're organic of course) through one of the digsites. Even if you're not going for Psy Ascension, that tech has a pretty useful passive bonus of -10% empire size from pops and is quite hard to get if you're not spiritualist and fishing for it with the appropriate scientist. This also means that Zro Distilation and the pretty big economic boost you'll get from harvesting all the Zro spawned by other digsites is only one rare tech roll away.
Is that on par with a free ringworld? Well, it's probably nowhere close. But it's certainly not "COMPLETELY useless" either (unless you're a machine, then that's almost true).
Overall... in a vacuum I actually like how it's designed since it actually gives you a reason to diverge from your original plan... but I totally understand why people find it annoying. It's the only one that pushes you towards a specific playstyle, while the others just give you something that's, more or less, universally useful. I'm not sure a Precursor is really the right place for such a mechanic, especially when it can trigger for empires that really have no use for most of the bonuses.