This is certainly a difficult answer to answer because there are several factors involved.

I particularly think it is necessary to a certain extent, if a team has the ability to sign outstanding players per season they should do so to strengthen their roster, but when they reach the point of one outstanding player per position it would no longer be necessary to focus the priority of signings on this small group of outstanding players, but focus on giving depth to the roster with players that can do a good job on the field without the need to be celebrities.

In this way I think you would have a strong balance between starters and substitutes without affecting the performance of your players. To cite a current example, what is the need for PSG to sign both Keylor and Donnaruma, both can be starters, that rather than fostering competitiveness hurts the squads, and affects the play of both goalkeepers.