The majority of games that come out are 3rd party games. They're not all of a sudden going to start becoming more optimized the longer this generation goes on.
Actually that's what happens when they figure out their own in-house engines. Look at Rockstar, they went from Red dead Redemption which used their latest build that came off from GTA 4, and was retooled from the bottom up. Then with that retooled they were able to make GTA V look the way it did on PS3, 360. There's a huge progression in how character models, animation look from gta 4, RDR, and GTA V.
Same goes for DICE's engine, even though to push their latest build they sacrificed resolution to have better lighting, textures and effects.
Go look at Naughty Dog, look at how Characters look in Uncharted 1,2,3 and then look at last of us.
Huge progression of their tools, engine and rigging work.
Third party outside of the few I mentioned seem to get caught up in just trying to one up in each game and try to make a new engine for each one.
Or they don't try to improve their code, and build a shitty engine around it aka fallout 4.
Seriously go look at the past 2 years of call of duty compared to ghosts. Look at the progression in engine, or changes they made for each studio. Each one runs it's own built variant of the COD engine.
Some of them better than others. treyarch goes for almost cartoony, high hue color rendering which is why everything in that game kind of pops color wise.
Sledge Hammer went for the crysis mantel in how they rendered their game assets. If your rig can play it it looks pretty damn impressive.
You don't think as time on they don't refine? That's my whole point that's proven with titles in last gen, cause they do.
Look at xbox in the beginning of 360 they had HD component and most games after HDMI were still 720p, then as U3 for gears, and(bungie's halo engine don't remember what it was called) got better with xb360 documentation and updates to skd's we got more 1080p outputted games.
Gears of war 3 still looks freaking great character model and effect wise.