I would say that Moiras damage lock on should be the same distance as her healing spray. But other than that, she is only effective in certain situations. If your team isn’t all grouped together - for example you have a flanker, a diver and such - she isn’t going to be as effective heal wise as a different support.
Not to mention, if a Moira is really your biggest issue in a game, a dVa can easily eat her orb from having any effective and a decent sniper can force her to either fade or get one clipped. Her ult means she can’t fade or duck making her an easy pick.
Another support that can give her a bad time is Ana. Sleep her for your team to get her, grenade so she can’t self heal or heal her team mates and you can hurt her our of damage from her.
The problem isn’t that she’s difficult to counter, it’s mostly that people either don’t put their attention on her or try to play around what she does. Play a distance from her and she has to rely on orbs to hurt you which means her team is getting less heals as she’s wasting her orbs on you.
Regarding the 10k damage - that is very circumstantial. Were they all graved together? Was the Moira nano boosted? How long did the game last? Was she the only healer on the team? All these things that contribute to those stats.