Rubber, glue
Again, not my opinion.
Look around: who voted Trump into office?
What thoughts voted him in?
I doubt they're anti-capitalist.
But [wealth] is a problem
Again, many don't share your anti-capitalist sentiments.
They'd say the problem is cronyism such as political connections & undue influence of moneyed special interests in politics.
These are not the same.
They aren't opposed to accumulation of wealth.
They're opposed to wealth gained through illegitimate means (eg, connections to win government bids, pass laws in their favor, capture regulatory agencies, reduce competition): economic government corruption, ie, crony capitalism.
They boil down to the same answer: get money out of politics (eliminate the dependence of campaigns on fundraising, reform lobbying) & break up the 2-party system.
If we believe wealth inequality is the source of the issue
Many think it's a symptom: the problem is political access from wealth disadvantaging others from gaining wealth or crony capitalism.
“A presidential cabinet position shouldn't be for sale to the highest bidder” is more direct without requiring buy-in to an idea many don't accept.
You focus on wealth rather than that no level of wealth should be able to buy that sort of thing.
one is addressing the actual issue
Questionable: the actual issue is illegitimate power as originally stated.
Some people care more that it was gained at all: they shouldn't have that illegitimate power through wealth or any other means (personal connections, favors, etc).
They want the cronyism removed from capitalism.
so nerfing your messaging and platform
It's not: it's framing the same goals in language other voters will accept.
Neither oligarch nor kings implies capitalism as you stated.
Democrats will not win on the messaging being proposed
Until Democrats build in other states the kind of establishment they have in California & New York, Democrats in other states will need to adapt their message to their voters.
Frankly, adapting a message isn't enough.
They need to beat Republicans at social media, have their own answer to right-wing influencers & podcasters like Joe Rogan, probably pump out their own viral bullshit, answer Republican troll farms with Democrat troll farms.