I understand where you're coming from. I truly do. There are nostalgic people who say that the animation back then was better than today and it is nostalgia. Now when it comes to things such as Tiny Toons Adventures and Animaniacs, yeah animation has improved since then. Animaniacs can still stand up due to its writing and humor, but as far as animation goes it is held back a little, not much, but a little.
Now you brought up the Looney Tunes as an example, in which case I have to disagree with you. That was some stellar animation and is still appreciated by many different animators even to this day. The timing, the pacing, the lighting, everything moves so well and looks amazing. Now I wouldn't say that it is better than animation we have today, although it is better than some animations, at other times it's not.
I'll even use the 90's as an example what is usually used in this case. Looney Tunes animation still stood the test of time and could play well with the other cartoons at this time, it was a better style than that of Rugrats, Hey Arnold, Cow & Chicken, and especially better than Ed, Edd, & Eddy. However Animaniacs animation (although directly inspired) was better than Looney Tunes and so was Batman: The Animated Series animation.
You see how that works? Can it still stand up, absolutely, is it better than what we have nowadays? Yes and No. I would say that Looney Tunes animation and some of the 90's animation surpasses that of cartoon animations such as Johnny Test and Regular Show. However animation from shows such as The Looney Tunes Show and My Little Pony: Friendship is Magic is really great work in animation.
What makes a cartoon show great though is more than just its animation though.