Those who continue to support Trump will hear Conway's garbage and agree with it even though it makes no sense at all. Of course you are 100% correct that the only way we have to form an opinion regarding a person's character, personality, attitudes, etc... it by observing their words and actions over a period of time. People have the capacity to change their beliefs and attitudes, and to modify their behaviors as well, but there is typically some motivation for them to do so.
Here is what we know about Trump from his words and actions (mind you, this is over decades, not just recent).
He was sent to military school by his parents who felt he needed more discipline (granted, that could be more about the parents than the child).
He went into business with his father and continued discriminatory practices toward Black, Latino, and other minority tenants prompting an investigation into his practices which resulted in a settlement.
He bragged throughout his young adult life about how sexual promiscuity, going so far as to create fictitious people to call in to local radio and news papers to sing his own praises.
He has repeatedly made deals with small business owners, only to renege on those deals and not pay the agreed upon wages. Many of those small businesses had to fold or were greatly diminshed.
He cheated on his first wife (who also alleged, then recanted), sexual abuse in their marriage. As part of their divorce settlement, there is a gag order against his first wife.
He cheated on his 2nd wife as well causing a second divorce. Similarly, his second wife has a gag order as part of their divorce settlement.
When his daughter Tiffany was 1 year old, Trump made statements which appear to be sexually objectifying her (I.E. discussing her legs and potential breast size).
He has made demeaning statements to women (Rosie O' Donald, Miss Venezuela, his wives and wives in general, Carly Fiorina, Hillary Clinton, Megan Kelly) calling them dogs, fat pigs, stating that their role was only "to make sure dinner is ready", and equating menstruation with illness causing crazed behavior.
He has lied habitually, even going so far as to tell people that he had lied about statements he had made repeatedly.
He mocked a disabled reporter.
The list goes on...
Sometimes generally good people do minor or even major things that cause people pain. We all do, because we are human and we can be selfish at times or lose sight of what is important. We are all subject to those problems because we have to balance our needs and desires with those of other people and life is messy.
Sometimes seemingly good people for various reasons, do something very bad (I.E. John Edwards and Anthony Weiner come to mind). They lose esteem in our eyes and our relationships with those people changes or are terminated. We have to re-evaluate what those people were motivated by and what would lead them to such a disregard of the commitments we make to each other. We wonder what is in those people's hearts (I do not like using those colloquialisms).
Then there is Trump. Unless he has some completely separate life that he is really, really trying to keep secret, in which he is a generous, loving, gentle, respectful person (you know, the exact opposite of what he is showing), then we have to go by what he gives us in his day to day actions and words.
For Conway to request that we disregard what Trump does and says and go to some mythical place where we see "his heart" is beyond ridiculous. Trump is showing us, every day, what is in his heart. Picking cabinet members who go against the very nature of the departments they are supposed to lead shows us what is in his heart. Standing up for a foreign dictator instead of acknowledging that major espionage has taken place, shows us what is in his heart. Going after people like a petty bully, after legitimate criticisms, shows us what is in his heart. Since we cannot read minds or hearts as it were, the only thing that shows us what is inside of a person is how they behave.
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