Yes, I get it, modern ECT is very much improved.
However, I don't recall even implying or "act[ing] like the alternative is some kind of panacea", and I don't hold such a position, and I don't say there is no cost in the alternative.
In fact, it is likely that both are major problems, and will at some point be considered barbaric (as will the cancer chemotherapy you mentioned).
All three are deliberate massive disruptions to the entire system, not at all targeting the actual problem, and in fact any benefit is simply a welcome side-effect. An analogy would be a problem in some towns in the midwest US, and ECT is like hitting the zone with a Magnitude 9.3 earthquake and Ketamine/Chemo is like hitting the zone with a massive flood. Sure, the problem may go away, but...
The best advances are being made in immunological cancer treatments, which are far more targeted, and looking far more effective.
Eventually, we'll be able to know more to know which small subset among the 100 billion neurons and ~quadrillions of synapses to target. Meanwhile, considering either ECT or systemic drugs as much more than a few steps up vs applying leeches is just wrong. I haven't seen a shred of research that indicates understanding of exactly what brain structures are being targeted, and why nevermind what neurons, for ECT or the systemic drugs, and quite a bit on basically empirical, 'well we do this and it gets a desired effect X% of the time'. Sure, that is way better than nothing, and it is all we have, but it is NOT anything like the desired end state of diagnosing IN DETAIL and EXACT problem and it's detailed mechanism, and then repairing it.