You wouldn't be drawing the game out to salavage points, you would be doing it to deny the enemy ppoints, a slightly different objective. As for dropping the objectives deep in the slow armies corner if you have a 'fast' army such placement shouldn't be a problem for you.
I deliberately didn't inlcude siegers in corners as yes, unless your army can drop ont he artillary you are just going to get shot enough - everyone should now know a wide frontage is the worse thing to happen to a siege army
But by making 4 turn games a lot worse than 3 turn ones you are altering peoples army picks. You have to have a fast enough army, so it does alter the 'meta' game. Sure 3 turn games are better to fit into the time availible but if every army was a fast one it would make the selection a bit narrower and I think also a bit more boring.
You also make things more restrictive for future lists - they will have an aspect of being able to shift enough stuff into winning positions into 3 turns rather than just denying positions (which as you point out has its own risks).
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