Internal math at my org says that lambdas cost about 20% more than an equivalent amount of EC2 power at full utilization. Now hitting full utilization is very hard, but the point is that lambas are only cheaper compared to underutilized EC2 hosts.
That's ultimately the misuse 9f the technology though right. Unless it's a freak, business changing, spike in usage due to exposure or whatever that lambda are not critical path suitable and don't seem to have been implemented with that intent.
For example if your sign up process is lambda you did you got your cost benefit analysis wrong on anything other than a prototype or mvp, but if your 'change your profile photo', something that maybe happens a handful of times across a month on average per user at best, and you implemented that as your lambda to reduce load and delay scaling needs on your core infrastructure then that feels like you did it right.
Any many people (like me), think Kubernetes is a better way to increase utilization compared to Lambdas. Especially with things like autoscaling, you can keep a kubernetes cluster pretty highly utilized, and no cold startup dance.
If you don't scale up at 80% usage you either have extremely non-volatile workloads (in which case, yes, of course, use EC2s), or you're doing it wrong.
