I agree with some of that but in my opinion we appoint coaches and managers (and directors of football now) so that we don't have to 'see how they do'.
We should be looking at DCL in training and pre-season and deciding if he's ready to be an important player for us, not giving him an entire season and then deciding actually he wasn't up to it after all. We should be looking at Tosun and deciding if he has the underlying ability to hit 20 goals, not just saying well he might do better if we give him more chances. If we're going to start actually achieving things we need to start being ruthless and implementing proper plans, not doing even more of the aimless meandering we've been doing for the last few years on the basis that things might come good if x, y and z happen.
Wouldn't argue with that, but we don't have a bottomless pit of money to bring in every player we need, plus we have a lot of deadwood that needs moving on to free up salaries. For me our priority has to be, in order, LCB, CM, LB and AM. They also HAVE to be good enough to go straight in to starting XI. We already have enough young squad players that need further developing.
I also think you are expecting an awful lot out of our coaching staff if you feel they can make those decisions on DCL and Tosun, based on 6 weeks training (half of which will focus on fitness) and maybe 4 pre season games in which each player will probably get no more than 45 minutes. All this whilst trying to introduce a completely new system to the team. the last thing I want is us making hasty decisions on them and the have to make further hasty decisions in the transfer market given that it closes in early August.
As regards Tosun, who one would imagine will go into the season as our starting striker, you want us to be reasonably confident he could get us 20 goals a season. If not, presumably you think we should bring in somebody who could. Well in the last 5 years there have only been a total of 9 players who have scored more than 20 goals in a season. Suarez, Aguero, Kane, Lukaku, Salah, Vardy, Sanchez, Costa and Sturridge. Think on that for a moment.
As regards DCL, IMO he should go into the season as back up to Tosun, with the emphasis being on developing him through limited game time and personal 1-1 coaching centred on his weak areas.
Come January, if it turns out we have a serious problem in the striking area, then we can look at finding a fix then. But for me, there are more important area's to deal with this summer.