Zero plastic doesn’t need to be a goal. There has rarely if ever been a more versatile and useful material. Delivering food and medicine to humanity would be impossible if we all woke up tomorrow without plastic.

So it’s more a case of judicious use:

1. use when no feasible alternative exists (not just because plastic is most convenient)
2. invest in effective recycling and recovery programs, including total incineration - AND (important) make sure the cost of this is shifted upstream to the manufacturers of plastics

There will be many cases where “no feasible alternative exist” and that will mean “it is prohibitively costly to do it with glass and steel.” I think that is really your questions. The answer is yes, sometimes plastic is actually best.

But I’d feel much more comfortable deciding that for a given use case IF #2 actually existed. Under current conditions, there may be no reasonable use of plastic at all.