Slowness reads as carelessness
A visitor cannot see your test coverage or your hosting bill. Load time is one of the few signals of engineering quality that reaches them directly, and they interpret it emotionally rather than technically.
A premium claim delivered by a sluggish page creates a small dissonance, and dissonance is expensive when someone is deciding whether to trust you.
The usual culprits are content, not code
In practice most heavy sites are heavy because of unoptimised images, a stack of third-party scripts nobody owns, and fonts loaded four weights at a time.
None of that requires a rewrite to fix. It requires someone to take responsibility for the page weight and keep taking it.
Set a budget and defend it
Decide what the homepage is allowed to weigh and what it is allowed to load. Then treat additions as trade-offs rather than accumulations.
Every marketing tag has an owner who wanted it and no owner who is accountable for what it costs. That asymmetry is why sites get slower every quarter.