Being kind, thoughtful and considerate are all great, lovely qualities, can really help a team to work well together and can help set a positive culture in the workplace, so you are doing a wonderful, positive, constructive thing. 'Own' that and don't let anyone take it away from you.
What comes out from your posts though, is that you have a very binary view of workplace behaviour, as either 'lovely', or 'openly horrible'. You don't seem to have any idea what polite assertiveness looks like, never mind how to do it. Standing up for yourself, asserting your limits, can be done nicely, politely and with charm.
The fact is, people respect people who say no sometimes and with ease, far more than they respect people who say yes all the time (and might struggle to complete the task, fail to do another task, or fail to look after themselves).
Within a team, one person being 'too nice' can be a liability, because they fail to assert the team's boundaries and might end up agreeing to take on work for other people that isn't really the responsibility of their team.