I love cod and I've bought each one , but I believe that letting players "pick 10" and letting players pick whatever they want leads to very monotone and self-minded game play. Siege is in a unique position that you actually need to know what your teammates and opposition is planning for. I hate to say this but it reminds me of a fps dota/lol. You decide what you want to do at the start of the game and you vey damn well play your position.
I agree with this analogy a lot, it is like choosing champions in a lot of ways. Limiting each operator lodauts also helps balancing each gadget. As an example, the lack of assault rifles on defenders is probably to give the attackers advantage on mid/long range.
In fact, since defenders can camp, they have the advange so attackers have better guns and gadgets in general because of it.
Pulse's heart beat monitor would be pretty OP as a attackers gadget for example, as a defender is good but you put yourself in a lot of risk too.
Defenders with shields would be crazy too, or having 4 mounted LMGs, etc
The operators setup, basically serves as a balancing tool and as team building tool too since you can know pretty fast what your team mates cand do.