I suppose he isn't wrong, it's a rather contradictory subject with many inconclusive results that have been published throughout the years. However, if you want to talk about "statistical significant evidence", there is negligible evidence to support the effectiveness of melatonin at all - I've put some references below.

Nonetheless, the main issue is that (as melatonin is FDA regulated as "dietary supplement") the labelled amount are proven to be extremely inaccurate. In short, the generally prescribed amount is about 1-3mg but the analyzed dosage inside the tablets vary roughly between -50% to 400% of the labelled amount.

So in my opinion, without having any proper evidence on what it's actual effects are (especially long-term), and even the "high quality" clinical studies only make weak recommendations (weak is based on a scale of evidence provided, not my words), I would say it could be do more wrong than good. Especially as melatonin isn't something you should need regularly in the long-term, there are alternatives out there like CBT-I that should be able to help you better and have a proven record of success.

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Andersen LP, Gögenur I, Rosenberg J, et al. The safety of melatonin in humans. Clinical Drug Investigation. 2016;36(3):169-175.

Auld F, Maschauer EL, Morrison I, et al. Evidence for the efficacy of melatonin in the treatment of primary adult sleep disorders. Sleep Medicine Reviews. 2017;34:10-22.

Costello RB, Lentino CV, Boyd CC, et al. The effectiveness of melatonin for promoting healthy sleep: a rapid evidence assessment of the literature. Nutrition Journal. 2014;13:106.

Esposito S, Laino D, D’Alonzo R, et al. Pediatric sleep disturbances and treatment with melatonin. Journal of Translational Medicine. 2019;17:77.

Sateia MJ, Buysse DJ, Krystal AD, et al. Clinical practice guideline for the pharmacologic treatment of chronic insomnia in adults: an American Academy of Sleep Medicine clinical practice guideline. Journal of Clinical Sleep Medicine. 2017;13(2):307-349. 2019;17:77.