I'd heard that zinc is most important in cam break in, once broken in it's a lot less critical. That would be for stock cams, people with high spring pressure/steep cam ramps would know better.
Anecdotally, I've run Mobil 1 synth oil for most of the last 22 years in the AMC 232ci six in my '63 Rambler Classic. Dead stock, and broken in looong ago on dino oil. Zero problems, though I think in the next year I'll send off for an oil analysis just to look-see what's going on down there for wear on the hard parts.
I'm about to break in a brandy-new Rambler 195.6 OHV six, new cam and lifters, stock valve springs (comically soft rate!) but I'm using 4 qts of Joe Gibbs + 1 dino oil. Would rather waste money on needlessly good oil than regret, etc.
The 5th qt of Joe Gibbs will go in the first oil change as an "additive".
