Spot fleets are really powerful but they take a lot of parameters and are quite hard to get configured right.
But running standalone spot requests is indeed much worse.
Autoscaling groups come much more natural to people, it's just that the native spot implementation is unreliable.
I mentioned before in this thread that I implemented a tool called autospotting that allows your on-demand autoscaling groups to be automatically converted into a sort of spot fleet, by replacing their members with the best available spot instances.
You get the best of both worlds: easy configuration based on your group settings, so you don't have to worry about bid prices, instance types and weights: the bid price is automatically set to the on-demand hourly price of your original instances, the instance type is also automatically determined based on the original instance type, so you can get any other type that's at least as large, even from a different generation, the selection is currently based on the lowest price, so you will pretty much automatically get various types without explicit configuration. When no spot instance types are priced lower than the on demand price the group will happily run the initial on demand instances until eventually some become available for a better price.
Gradually these spot instances are launched and attached to the existing group, and on demand instances are terminated to keep the capacity constant.
Unlike the spot fleets, this supports out of the box anything that is backed by autoscaling groups, such as Elastic Beanstalk, Kubernetes clusters built using kops, environments managed by CodeDeploy, and so on.
And unlike spot fleets, the migration to spot and back is a matter of setting a tag on the group, so you can easily revert back to the original group configuration if you decide to.