At Lumin Health, we treat about 80% of our patients with esketamine, and the rest with ketamine (generally only if they don't meet esketamine criteria). After the initial course, patients tend to find a good balance of ongoing care that helps treat their particular depression / depressive symptoms. This happens less with ketamine since it tends to be prohibitively expensive to continue care (upwards of $1k/month).
There is a long-term trial now in its 4th year with esketamine (https://clinicaltrials.gov/ct2/show/NCT02782104). I'm not sure how much has been published yet, but early data I saw supported immediate relief and long term benefit over the 4 years.
In terms of it being a sinister ploy by pharma, it's definitely priced higher than its ketamine generic counterpart, but for the vast majority of our patients, ketamine treatment out of pocket (since its not covered by insurance) is absolutely unaffordable, and pursuing the insurer-covered version of treatment is a high-value option.
A lack of physical dependence should not be interpreted as addiction-proof. Nobody is physically dependent on gambling, for example, but gambling addiction is prevalent.
Ketamine has been a party drug for quite a while now, and as far as I know, hasn't been shown to be particularly dependency-inducing, though low-dose ketamine over the long term might be (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6236511/)
Also, as far as I know, ketamine treatment isn't intended as an ongoing medication, like an SSRI, but as a treatment for acute episodes of depression. I might be wrong about that; webmd says, "For treatment-resistant depression, patients usually get the nasal spray twice a week for 1 to 4 weeks; then once a week for weeks 5 to 9; and then once every week or 2 after that." However, the use-cases I know about (from talking to researchers studying it) is as an intervention to prevent suicide during severe depression (since it's relatively fast acting).
As always, its a cost-benefit calculation, that should be carefully made in consultation with a professional. The cost of severe depression can be quite high.