First off, people need to stop comparing every Medic to Caira. They aren’t the same. If they were the same, there would be no reason to even have the other Medics in the game. I main Slim and Val for a single reason: I enjoy their playstyle. Caira may be the strongest healer, but she lacks depth of play.
Caira basically just spams healing grenades, which is great, but that’s really all she is good at (beside the occasional speed boost). She is a great Medic, but I find her kit boring. People complain about Val, Slim, and Laz way too much, and that’s because they aren’t just straight Medics like Caira is.
Lazarus focuses on letting teammates die, and bringing them back to life without strikes, while also being able to leave weakspots.
Val focuses on single target healing, slowing/marking the monster with tranqs, and leaving larger weakspots (also doing considerable damage).
And Slim, he is more of a versatile Medic. He can be straight up in the Monster’s face, dealing heavy damage and healing everyone often. Or, he can sit back, fire accurate shots from a distance, and throw healing bugs/bursts out when he can. People need to be utilizing his spore launcher very often. You might think a good Monster can make it useless, but if you are able to blind their smell then juke around bushes or rocks, it can make it very easy to lose the Monster if it is focusing you (despite it also working great with cloak).
Honestly, I think it has more to do with people not adjusting properly to the other Medic playstyles, rather than a certain Medic being weaker. I have never had problems winning with any of them, but they do take some practice. I would also like to state that Caira’s skill cap is MUCH lower than the other 3 Medics imo. She is super easy to pick up, whereas the other Medics have very particular playstyles that take longer to get used to.