Want to know who it helps when you tell a griever to get over it? Exactly one person - yourself. It leaves you feeling helpful and self-righteous, but at best it is useless to the one who has lost, and at worst it harms them and stifles the healthy process of grieving.
You think that grief that has gone on longer than makes you comfortable is complicated grief (a mental health diagnosis that I think is unrealistic and unfair)? I say that complicated grief is the grief that has been suppressed, often at the advice of people like you, and is forced to come out later in very unhealthy ways - like alcoholism, drug abuse, eating disorders, anger, and a variety of other addictive behaviors.
So your suggestion to "get over it"? It is essentially a suggestion to halt the healthy, natural, and needed process of grieving - which may take years, and may never be fully completed - and so force the sadness to turn inward and become septic instead of being outwardly expressed in a healing manner.
Grief exists for a reason. You don't like how I allow my grief to run its natural course? You get over it - or at least keep your mouth shut. If you can't muster up a bit of sympathy or manage a polite "I'm sorry," then both you and your grieving friend or family member would be better off if you said nothing at all. Your guilt trips are not wanted here.
Do you think you'd grieve "better" (which is really your code word for faster and more conveniently), or that you have dealt with your own hardships "better"? If you feel healed, then good for you. But grief is not a competition. Stop trying to turn it into one. There is no one right way to do it, so quit heaping guilt onto other grievers about their feelings. I'm tired of hearing of these hurtful things being said to my grieving friends, and of having them said to me (much more occasionally, thank goodness). Comparison is useless, so cut it out.
Nobody wants to feel grief. But for those of us who have lost and have the courage to grieve healthily - we do this because we have to, not because we want to. Certainly not to put you out, so quit acting like that's what's going on. This is a matter of survival.
Want to be actually helpful? Here's what to do - shut your mouth and open your heart. If a griever has trusted you with the intimate vulnerabilities of their loss, listen and acknowledge. No matter what you think they "should" be feeling, this is what they are feeling. So pay attention, and keep the judgements to yourself. How can you be sure you know what's best for them anyway?
Does that make you feel uncomfortable? Good. Like I said, that's normal. Death sucks for everyone, and so does grief. Deal with it.