Why are you using other examples when the facts are right in front of you?
"I am bad at Sage mode"
Minato fans: " Oh he didn't mean that, he meant that he is worse compared to naruto but hes still the best"
It's absurd to think this way, specially since the author himself made it clear that minato's sage mode is terrible. (He himself admitted it)
I use other examples for the reason i mentioned. You completely skipped the following sentence
"Actually i'm not good at senjutsu"
"It takes too long to kneed the chakra and i can't maintain it for long"
1- The first part of the sentence is to establish the fact that Minato isn't good at senjutsu
2- The second part of the sentence is to explain the area in which he isn't good at
The reason he isn't good at senjutsu according to his own opinion is because it takes him longer time to build up the chakra and his time limit in SM is also smaller than usual.
Doesn't change the fact however that he still control the chakra perfectly(judging by the pigmentation of a true sage) and can use it in battle. The thing i'm trying to explain and that you people keep ignoring and still will