Confirmed. Development happens through dev plans and form. The training sessions definitely can impact it though because morale and form have an impact on how fast your dev plan takes to finish. The new training is all about the sharpness and fitness.
It has a lot of perks. If you have a lot of games back to back, you can actually choose to take rest/recovery days so your 1st team is fit for games on a short turnaround. In the past it always took strategic subbing or a full 2nd squad to go into UCL games with full stamina. Now it's easy.