The standard should be amended for the modern web then. AWS's (and I'm sure many other's) implementation of this for their various load balancing, CDN services, etc. are critical to the health of the web now.
From the DNS client's perspective, there is a positive and a negative.
Positive: since the server with an alias record actually returns an A/AAAA, a client doesn't have to contact any more servers to get the results.
Negative: the servers for the CNAME target may be faster, relevant if the name is used beyond the A/AAAA TTL but sooner than the TTL would be set for a CNAME); or the servers for the target may be providing much finer targeting than is possibly by proxying.
It's a not standard and therefore, is not a generally applicable solution.
When something not standard becomes common practice and is expected, here comes the pain.