Originally posted by h1a8
In comics, a character never holds back his/her power unless stated or shown explicitly.
The hell you been reading man? It hardly ever says a character is holding back. It is very common for more powerful foes to hold back against weaker characters. This does not means we assume that a character is holding back automatically. A good indication of not holding back is when characters are in a close fight and both character seems to be trading blows. This never happens to Thanos he always destroys his opponents or he is fighting someone out of league.
You can have a fight between character A and character B and you only found that Character A was always holding back many comics later/years later... it's a common trope.
It's like Dragon ball Z you find out someone was only using 30% of their power way after the fight is done.
Thanos was never stated or shown to hold back when he attacked someone. So it's fair to say he is using most of his power behind his punches. It's not like he's thinking "I better hold back so that I don't kill them".
Here Adam Warlock saying that Thanos's might has never been fully been testing.