I agree with you, Arsenal should avoid wasting time pursuing just one uncertain player, considering that time is more valuable in finding alternatives with comparable talent.
Nicolas Jackson might be a better alternative if they fail to land Gyokeres.
The problem is, Manchester United is also eyeing the Chelsea striker.
If Arsenal were to make an offer to Jackson, I'm sure he'd choose Arsenal over Manchester United.
If Jackson weren't so concerned about the size of the offers from both teams, it's certainly possible he'd choose Arsenal over Manchester United, as Arsenal's performance last season was far superior to Manchester United's. However, Jackson wouldn't be wrong if he wanted to join Manchester United, as the team will also make more effective changes next season to improve their performance in the Premier League. A player like Gyokeres is certainly worth acquiring for a big team like Arsenal, although other alternatives are also worth considering.