>There are more sickness inducing things in air, water and food.
I mean, just no. Unfortunately I don't have a time machine to kick your ass back 300 years ago to a city like London so you get to experience it for yourself.
The claim is twofold, that London, a major capital city, arguably the largest most important city at that time, had little to no functional sewerage, turds floating down the Thames, people drinking cholera straight from the pump, etc.
Which was true at that time.
The second part of the claim is that is no longer the case for London, and somewhat implied is that few other large capitals of the world have such extreme issues now as London has had in the past.
London may have cleaned up, but that'd be a stretch for several large modern cities in India, South America, Indonesia, etc. that are straining their civic infrastructure or applying unevenly.
Globally, in total mass (or other measures) environmental pollution is "worse" now - just largely less visible (pushed from the G20 out to other countries) or dismissed (carbon dioxide is good for plants!! (etc.)).
What exactly are you claiming? Environmental pollution was more 300 years ago than it is now?