From what I've seen, it's usually VP and above who actually see the bonus numbers worth talking about. the people doing the heavy lifting day-to-day? Peanuts if anything.
I've worked with a couple of agency holding groups where the media buyers were hitting $2M+ monthly spend targets and still getting nothing beyond a pat on the back 💸. meanwhile, the VP layer picks up the big cheques regardless of whether the campaigns actually made money or just burnt retainer hours.
WPP isn't unique there - it's the same story across most of the big groups. Unless you're near the top of the pyramid, don't hold your breath.