Arsenal has two strikers available, Havertz and Gabriel. They don't mind adding a new striker. They think those two names are enough to help them this season. They are focusing on other positions, not the striker position. They scored a lot last season. It's probably their reason to feel confident enough with their available strikers. And they decided not to sign a new striker.
I also think that it's not a problem for Arsenal when they don't recruit a new striker, although it wouldn't be wrong if Arsenal wanted to recruit another new striker to replace one of them if they get injured during the season. However, the reason you said could also be very logical because Arsenal also thinks more about other more important lines such as the midfield and defense so that the opposing team will not easily break into their goal when competing in any competition.
Except for a sense of incompetence at any point, i don't think Arsenal will be needing to add more strikers to their team as that which they have got already is really doing well and supposed to be considered enough until the end of the season probably when any of them eventually wants to move then they can be replaced by scouting for a new replacement for them. Gabriel have been of a very good brilliance that i consider him doing well as well as Havertz so probably till next season Arsenal may not be needing any new strikes. The midfield should be their point of focus and attention now.