> All you need to track a user is data you send as part of a HTTP request.
Browsers impose a limit on concurrent requests (usually 6 per hostname) for a reason - HTTP requests, be they too many or too large, are one of the largest performance problems in a typical site. Just because it's easy to fire-and-forget an HTTP request doesn't mean it doesn't have a performance impact, especially in apps that are already network-chatty. I think you know this because you go on to list "the volume of data we're transferring" as a performance bottleneck, and obviously that's done through HTTP requests. Also, in the real world analytics installations virtually always include installing a third party library i.e. google analytics, so you're taking hits to download the library, interpret the source, run the code alongside your app, usually in the same thread, all before you've fired any of those HTTP requests.
> A/B tests just means settings/feature flags and metrics
I'm aware of the definition. If you are implying that conditionally loading settings or feature flags and tracking associated metrics doesn't have a performance impact, I would disagree. It is usually possible to implement a given A/B test with minimal performance impact, but in practice these are absolutely a contributor to the kind of bloat I'm frustrated with.
> sessions are recorded since ever with zero performance penalty
It sounds like you're talking about logs. I'm talking about "session replay" features provided by companies like FullStory and Sentry that allow you to replay every mouse move and keystroke of your users.
> It's trendy to shit on the status quo but it also is low-effort and lacks any insightfulness.
By this point in your comment I think you forgot what we were talking about. I was arguing that the architecture of modern SPAs shouldn't bear the blame for bad performance; my point being that whether or not we continued to use server-generated HTML we would still be suffering from similar problems of bloat today. The "status quo" that I'm shitting on is taking lazy approach to performance management and injecting way too much cruft; unless you work for an analytics provider I'm not sure why you would be opposed to that stance.
