Dariuszw, V2 isn't necessarily a best angle of climb speed. It's a scheduled speed that, if followed, will enable the aircraft to meet the performance shown in the performance charts. Those charts account for the various regulatory requirements, including obstacle clearance at various distances from the take-off point.
Accelerating from V2 to Vx doesn't happen instantly. Nor is it 'free' ie there is a performance penalty during the acceleration phase. In this case, angle of climb. During that *short term* reduction in climb angle the aircraft may no longer meet the net climb gradient that obstacles or the rules require. You are correct in the sense that Vx will provide better climb angle than V2, however *getting* to Vx initially results in performance that may not meet the requirements.
There is a case where increasing speed can improve performance. Or, more usually, allow a greater take-off weight: Using an 'increased V2' or 'improved climb' or similar language. This is used to get a better climb angle to clear an obstacle further along the take-off path at the expense of using more runway & provided there aren't any limiting close in obstacles.