All this complexity is about luxury and convenience.
Yes once upon a time a simple heater was enough.
Then someone added split heating and A/C with independent left and right controls. Then it was computerized with proper on board HVAC control.

Now apart from all the electronic add ons, the heater core needs to be in the middle of the vehicle with the evaporator nearby to give even distribution of comfort for the occupants; that in turn means it ends up buried in the dash.

Why did it get that way? Simple, you the customer wanted it that way and in dealerships and auto shows all over the country the public see the modern advances of one make over another and the pack goes the whole hog next year to out do the other for the wow factor.

Now its infotainment and basically a cell phone on wheels with navigation because no-one in the Western Industrialized countries these days can read paper map or find a grocery store without it.
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A heater core job sucks for sure. You should have gone with at least a euro spare part. But anyways you can do this job by the book or you can attempt the short cut method. Which would be to remove the bolts on the right side of dash. Remove the bracket on the pipes and carefully stretch the right side of the dash back. Enough to slide the heater core out.

What makes the whole job difficult is the screw holding the pipes together near the firewall. The screw is reversed with the head facing the dash. The point being you can't unscrew it. I didn't think of it at the time but someone suggested after the fact that you can remove this screw by simply using pliers and twisting it out by the tail end. Once removed you can easily remove the heater pipes and slide the core out.


This might all sound confusing but when you start digging you'll know what I'm talking about.

 

Yes book time is 6 hours and you need every minute to do it successfully.
But then a Jag XJS V12 is 23 hours book time to do a heater core.
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i dont think its a peice of crap. its just the way i talk. atlantic british had the o-rings but not the clamps. i already have the heater core out. in fact i put the new one in with the old 0-rings and clamps and pressurized the system and it leaked. the vehicle is still apart. and yes i am aware why the heater core is located where it is. again its just the way i talk.