First, you will NEVER see real MHz on cloud/virtual servers due to host OS which is designed to emulate real hardware instead of be the hardware.
Second, the charts you posted metered in ECU, not MHz.
I've made additional research, the results are below.
As you probably know, t2 instances have burst capability and during those bursts they run at more than 100% of CPU, however it can be measured in real tasks, not in MHz.
I run two instances: t2.medium and c4.large, as on the first screenshot of your video. All instances were created using the same Amazon Linux 2 LTS Candidate AMI 2017.12.0 (HVM), SSD Volume Type - ami-db1688a2
To create load I used https://github.com/phoronix-test-suite/phoronix-test-suite/ :
yum install -y php php-cli php-common php-gd php-pdo php-process php-xml
mkdir tmp; cd tmp
tar -xvf phoronix-test-suite-7.6.0.tar.gz
./phoronix-test-suite install pts/build-apache
./phoronix-test-suite batch-setup # (answers are no and no)
then run each of those tests three times
./phoronix-test-suite batch-run pts/build-apache
and recorded average value for each test, like here:
The results are in the chart, data are seconds, less means better:
The gain is ~20% which is les than on your screenshot but we don't know what tests were used by AWS (I asked but they didn't answer) nevertheless as you can see t2.medium was faster than c4.large.
p.s. I also run bz2 decompress test: t2.medium was slower there perhaps due to more intensive disk usage (I used the cheapest disk option).