[snops]

For production,its best to specify the important properties as you say, then let the contract manufacturer figure it out, rather than spend ages finding the cheapest 100nF 10V X5R 0402 cap. If it really matters, then add a "no subsititutions" column in your BOM.

For smaller prototype runs, PCB+Assembly suppliers like Eurocircuits have "generic parts" already in stock for common passive values, which they will give you for free.

Its only really if you are in a big rush or very budget constrained (e.g. a hobbyist or startup) that you would assemble yourself and hence buy all the parts.

If you do though, then Altium can happily manage multiple alternative options for the same "part" using ActiveBOM, including a search tool and distributor stock levels. I think the cheaper CircuitStudio option might have this too.