They need to adress the specialists first and foremost to eliminate the problem of them being duplicates.
Delete the voice-lines and names.
Names should be replaced with a generic specialist class like Grappler Specialist/Demolition Specialist/Wingsuit Specialist/Marksman etc.
Instead of having only 1 specialists, have them be as a Specialist Class that were trained at a secret training facility. That makes more sense as well because no one funds training for only one soldier at a time. They would train a group of soldiers. They could add specialist rankings for best specialist classes to create incentive and engage players to be the best in their favorite class.
Generally being able to customize your character within reasonable limits to preserve realism is a feature almost 100% of players want.
Distinctable with class, but customizable to stand out of the crowd and "make it your own" character.
Looking at Apex Legends, where the characters are so different physically that youre able to tell them apart even though they have similar skins or skins you've never seen before.
Apex: You can still see that it is a Lifeline even with custom skin.
BF: You should ideally still see that it is an Assault class soldier even with custom camo.
I think devs shouldn't underestimate small but impactful customizations like a gold chain, special boots, a distinctful patch, a scarf, motorcycle gloves, pilot glasses, dust goggles, a pack of sigarettes etc. These can be difficult unlocks as a show-off "bragging rights". Its stuff like this that makes you feel good about your achievements and showing off on the Battlefield.
Battlefield 4 had this on point with customizable gamertag icons which also showed up on your weapon and soldier as a patch. Players even figured out that if you covered a large surface of this patch with a distinctful background color, often pink, your whole character would turn out with a pink shade. Its stuff like this that players enjoy, but the core gameplay and atmosphere is what drives this type of engagement and is a positive sign of players thriving.
Example: Someone asks, "how did you get that cool scarf?" -"Its a specialist achievement unlock.". This small thing creates incentive to play the game and if its executed right, something cool and something that makes sense, this can be highly motivational.
I could talk for hours about this topic.