Personally seen a couple patients die despite receiving monoclonal antibody treatment, seen several that developed severe disease, also one of my good friends parent died despite receiving it. When there is a low probability of death, most treatments are going to look effective to those prescribing it, given ~98% of the population receiving it will not die from COVID. At best, it doesn't appear to be remarkably effective, based on my experience seeing these patients in the ER and ICU.
The currently available literature does not demonstrate any clinically meaningful efficacy, at least the way that it is currently being utilized, and it makes sense why that it is. Patient's have been infected generally between 4-8 days prior to developing symptoms, it then usually takes an individual an additional 2 days to get tested, and an additional 1-2 days to get set up with antibody infusion therapy. The majority of individuals will likely already have circulating antibodies by this point making the utility of antibody infusion therapy moot. The bambam industry funded trial was stopped early due to futility and then the data was tortured enough to find some semblance of maybe benefit, however, clinically meaningful benefit like death or development of severe disease was not altered by the therapy.
I'd imagine this would be potentially beneficial if given prior to symptom onset in individuals with extremely high risk exposures (living with someone who is positive) who have a high probability of severe disease; however, given how expensive this medication is and its suspected affect on vaccine efficacy, the cost:benefit ratio is just way too high.
A doctor whose opinions on medical literature I trust wrote about the currently available evidence for this therapy in the article I linked below.
https://emcrit.org/pulmcrit/followup-bamlanivimab/