No ECT is most certainly the most efficacious treatment for depression we have.
Talking therapies have a respone rate in depression of circa 40% [0], probably just slightly higher for antidepressants up to about 50% and faster [1], ECT respone rate is well over than even for those with treatment resistance but as high as 90% [2]. Vitally, the reposnse to ECT is fast and is often under 10 days.
The fact that ECT is burdensome, limited in availability and stigmatizing (which is why it's got so much legislative structure around it) is not relevant for it's efficacy.
This is spelled out relatively well in the UK's Royal College of Psychiatry statement on ECT [3]
> ECT IS A FIRST-LINE TREATMENT FOR PATIENTS ... where a rapid definitive response for the emergency treatment of depression is needed
This is because it works quickly and reliably to treat depression.
[0] https://onlinelibrary.wiley.com/doi/full/10.1111/acps.13335
[1] https://journals.sagepub.com/doi/pdf/10.1177/070674371005500...
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3650296/
[3] https://www.rcpsych.ac.uk/docs/default-source/about-us/who-w...