There will always be tradeoffs.
MP4 is a compressed media format. Compression requires CPU time. Compression of a real-time screen requires a lot of CPU time right as the video is being taken.
Uncompressed media formats generally require less real-time CPU processing, but they also take up a much larger amount of disk space, memory, and other resources and so can be just as hard on a computer as compressed media.
Due to the enourmous size of uncompressed media, there really aren't any uncompressed video formats. Audio is much smaller and so there are uncompressed audio formats. You really need to just choose the one that gives the best trade-off of size and CPU time and use that. Trying different codecs can also be helpful for speeding up the compression/decompression processes.
These trade-offs tend to just about balance each other out. The only reason to use a compressed media type is because uncompressed media formats are just so much larger in size.
And a P4 is really, really old by the standards of today's software, especially media software.
I have not worked with screen recorders, generally, but a google search of lightweight screen recorders showed a result called Jing, which is apparently written by the folks who brought us Camtasia, which is a popular and capable recording suite. Jing is apparently designed to help tech staff see what users are experiencing and send them video instructions on how to resolve their problems. As such, it is supposedly rather lightweight. And because of their target market, the output files are probably rather efficiently compressed as well.