however our avionics are very good (Honeywell Epic) and frustratingly on our particular type it generally does a good job.
I thought you´re on the Sovereign? The EPIC is a pile of horsemanure especially when it comes to VNAV and the like. (IMO only, of course) I sure hope there will be a Sovereign+ soon. (Collins Proline)
In Europe, I don´t plan anymore. Hundrds, possibly thousands of Sector - to - Sector handover altitude restrictions make any planning a joke. The 3 times ALT plus ten works fine where ATC won´t block you from using it.
Sometimes one just wonders what ATC planners do have on their minds. Like London: descend realy, stay down low for ages. When flying out again: fly low for ages.