Let me clarify; there's nothing wrong with mixing and matching settings and rulesets. But I wouldn't say I'm running Shadowrun if I'm just running a D&D5e ruleset in a Shadowrun setting.
I think at this point we have to agree to disagree, because we clearly have different ways of looking at this. I'm of the opinion that communicating the ruleset you're running is important because if I go to a D&D5e game with a PF3e character, nobody is going to enjoy that. Specifying the setting is important too, but the rules aren't an unimportant thing you don't need to specify.
Regardless, when I say "Shadowrun is not an entry-level TTRPG", I am referring to the ruleset and not the setting. There is nothing wrong with the setting. I guess you'd parse it better if I said that the Shadowrun ruleset isn't an entry-level ruleset?