the real, not so fun answer is it all depends
one box integrated units can be very good, but of course lack the flexibility to decouple the piece-parts - at the same time, they can be smart buys - for example an older gen hegel h160 has an older streamer/dac built in, but the preamp/amp section is still world class - so at $1700-1800 used now, the h160 will be a good buy even if you treat the dac as a throw-away...
streamer/dac combos have similar issues... dacs are maturing fast, lots of trickle down happening, oodles of connectivity options... streaming front end sand streamer protocols and connectivity formats may still have more room for development/format change over time (though many would argue that is rapidly stabilizing as well)
so it depends on the user, their desire for a la carte flexibility to change (at a real cost, as mentioned earlier), versus buy a good modern integrated unit, use a good music source - e.g. tidal or qobuz, and be ’one and done’, just enjoy the music with a minimum of clutter (and complexity and cabling and power supplies)...