My Android keyboard is probably lacking the proper dictionary
I think using the dictionary is cheating here.
and is probably less reactive than the native app installed by default
That’s weird. When I install keyboards I don’t notice slowdowns but rather improvements due to the mainstream solutions being extremely bloated.
Even a typing test on a keyboard is odd. My grandma surely gonna fail this test and not because she’s old, but because she doesn’t know where the different keys/letters are placed on the keyboard.
But that’s what the test is about. It’s not about how fast you can press keys. It’s about using your key position knowledge.
I tried it on a tablet with 1 Gb of RAM. Most likely your device has a ROM issue.