First of all, Paul is right:That requires banning multiclassing.
Second of all: You can make the level 1 feature of most archetypes into a Ribbon.Taking multiclassing into account players don’t necessarily get their subclass at level 3 either.
Warlocks in 2014 were balanced around getting their patron at level 1. Which is why it was a mostly ribbon feature (Temp HP on a killing blow, telepathy, point blank charm/fear) with a secondary ribbonette (Expanded spell list).
Just give the Fighter a level 1 Ribbon feature for the Eldritch Knight. Maybe a Cantrip and the Arcana skill proficiency. Then do that for all the other level 3 subclass characters.
Tadaaaaah. Problem solved.