Not all comparisons are bad; they are simply an acknowledgement that something is different than something else.
Most widow(er)s probably wouldn’t expect or want for you to be just like their late spouse, so there’s little use in wondering if you’ll “measure up”.
I don’t expect a woman I am dating, or even more seriously involved with, to “help me get through my pain and loss”, as it relates to my late wife’s passing.
I should have done that prior to entering the relationship. By the time a widow/widower enters the dating world, they should already be through the initial stages of grief and into the recovery phase of rebuilding their lives.
If the person truly is ready to begin again with someone new they will make room for you in their heart.