If you're getting X% merit increases every year and miss one, it will look forever as if you're underpaid relative to your peers. So people who take a long parental leave will have a permanent "pay gap" unless either the company pro-actively bumps them up (pay for the absent time as if they were present) or the employee overachieves to catch up (in which case they still have a pay gap relative to their overachieving peers).

Of course, there's also ramp-down and ramp-up time on each side of the leave. I'd expect a leave of 12 months is probably closer to a total productivity loss of 18 month, which will drag pay down further if there's a reduction to a second merit increase. If you take years off, as many do, staying home until the kid enters kindergarten, then you're probably looking at a massive relative gap when you start back.

But yeah, taking a year for parental leave is not a death knell for most professionals' careers. It will realistically result in a long-term salary depression relative to peers, though.