But the difference is that Dundee isn't radar-equipped and while the essential first step is to get you up to the holding altitude, if they have other inbound IFR traffic that has priority, they need to get it below you/you above it long before lateral separation becomes an issue. When they can only do Procedural Service that's difficult.
Procedure separation was and continues to be used and long pre-dates radar.
The commercial IFR would not normally use the hold; direct to D4 Garmin approach.
Once the location of the intruder is known (e.g. at the hold), no problem for the commercial traffic to stay clear.
flyme.