Don't use the QT H.264 encoder, use the native Adobe encoder.
M suggestion is what you should do (this is generally the case!)
PS : i tries animation but it was too leggy to play.
this is expected since Animation is a lossless codec which means you have enormous bit-rate most playback systems can't handle. this codec is for editing purposes so you won't lose quality after another intended compression.
Quicktime format and h264 compression it gives the warning for downscaling the video resolution to ~2k.
what version of Ae are you using? since CC2014 you can't encode a decent H.264 in Ae because the format is not there. don't use the H.264 under Quicktime format options - it's a buggy and poor quality codec. even prior to CC2014 if you use the H.264 format you only get 5.1 level constraints which can't reach 4k. as M suggested use AME.
you will need at least AME CC2014: Adobe Media Encoder CC 2014.0.1 (8.0.1) update: bug fixes, H.264 at 4K, new YouTube presets, and more | Creative Cloud b… where you can use level 5.2 there and it maxes out at 4096X2304 which is a little more than the 4K digital film standard 4096X2160 (not the 4k preset of Ae which is full aparture Film 4k 4096x3112). the consumer standard 4K is UHD 3840X2160 that is also called 4k 2160p and this what YouTube uses: Recommended resolution & aspect ratios - YouTube Help and probably what you should be using in terms of resolution.
you have a 4k preset in AME.
you can also render a lossless version from AE and use some other 3rd party encoder like Handbrake