Yes, with select setups and with at least a somewhat-modern chain, trim-free shifting is a wonderful reality, especially when hammering over hills in order to hang with a pack of riders.

Yet it was that I got spoiled by such a setup which forced me to adopt any needed measures to avoid ever having to trim the front shifter on any bike that I ride, even indexed front derailers, and yes, I do cross-chain!
I usually start by working with whatever chain is already on there, and then as 70sSanO described it is a matter of observation and little tweaks to arrive at full clearances for the chain without undue trauma or disfigurement to the front derailer!

Lastly, the narrower chain can go on to further optimize everything, and the narrower chain eliminates all traces of rub.

Chains have not gotten weaker with each narrower version. Almost every decent chain today is able to handle mountainbike drivetrain use, which is far, far more severe than any road bike will give it. Yet defective chains do occasionally pop up.

Inside width of various chains are not quite identical, but I've found that 9-speed chain seems to run on every road sprocket I have tried it on, even old Varsities. Certain cranksets space the chainrings too far apart for use with 9s chain without tooth modifications, but I get them all to work.

The biggest change is always when removing old 5/6-speed width chains, which are nearly 8mm wide, and replacing with 7.2mm chain (7-8sp) or 6.6mm chain (9sp). I have yet to use 10sp chain on any vintage bikes, haven't had a reason and they only cost more.