i think this is clearly a matter of taste because i think exactly the opposite of the old vs new. the old foundation fonts and buttons feel too chunky, while the new foundation sleeker elements look much nicer in the overall layout comparitively. i have no complaints about functional usage on desktop or mobile, nor have any of my users since i enabled it. 
i think you could give feedback to your admins as well and perhaps they could create another theme with the old changes? enlarging those fonts you indicated isn’t difficult with css. or you could use a stylus type scripting browser extension to add your own mods (i do that with all the discourse sites i visit, including this one).
edit:
for example, something like these:
topic header text
.extra-info-wrapper .topic-link {
font-size: larger;
}
related/suggest topic footer buttons see also below
.more-topics__container .nav {
font-size: larger;
}