To clarify, shareholders don't vote to fire a CEO, so a majority is only tangentially important. The board votes on these sorts of decisions, however shareholders vote on nominations for board members -that are put forward by a seperate committee. So essentially no one on the board sits there without Sweeney's approval right now (because he holds the majority of shares, and presumably would have voted against people he doesn't approve of). Even if Tencent had a majority right now, unless the nomination committee had previously put forward board members that strongly favoured Tencent, and therefore gave them a good portion of board votes, then it would be effectively useless.

There are technically ways you can make certain seats on the board have a larger weight in voting, but I don't know Epic's specifics and am going to assume it's pretty standard.