Where's your evidence they were "designed to be barbarians" - they have the most synergy with fighters. Relentless Endurance actively clashes with Relentless Rage and Savage Attacks has the most synergy with the Champion fighter. Half orcs are fifth on the fighter.You can't really evalutate the pre-Tashas races without considering what classes they were designed to be 'Iconic' choices for. That's why Half-Orcs can be considered a success in the same terms. They were less popular than halflings overall, but the most popular choice for Barbarains. Given that they were designed to be Barbarians that would seem like a success.
Now certainly, this method of designing races can and has been questioned (and abandoned), and I don't like it much myself, but it prevails in the periods for which data is available.
Even if they were designed for the barbarian (IMO terrible design) in 2017 they simply weren't the most popular race for barbarians. They were admittedly a close second... to the goliath. A non-PHB race. If that's your metric (I don't think it was the designers') then the half-orc must be considered a failure, losing what was supposed to be its niche to a non-PHB race.
The half-orc also performs terribly outside its niche according to the 2017 data, losing to every single non-small PHB race in all classes except barbarian and fighter, beating the halfing at paladin, and beating the gnome at ranger and monk. Oh, and only being mid-pack for fighters.
So the half orc is not only a one-trick pony it's not even as good at that one trick as a non-PHB class. I've been saying throughout this thread that the half-orc is the race most likely to be ditched for a race that does its thematic strengths better; either the full orc or the goliath.