This was discussed on FR threads last summer. You may be surprised to find that I agree with you on this point and said so last summer. If one subtracts the "denominations" that really consist only of a single congregation and subtracts the doubtfully "Christian" and scarcely "Protestant" African Independent Churches and similar groups elsewhere, one ends up with about 8-10,000 real Protestant denominations. I would ask Orthodox and Catholic folks to register this point and avoid the 30,000 figure.
But to you, friend, let me point out that the point being made by whoever used the 30,000 figure stands just as strongly whether the number is 8,000 or 30,000. You have scored a pyrrhic victory in the gotcha game.
The existence of, in addition to 8,000-10,000 Protestant denominations consisting of more than one congregation,is already a scandal and makes laughable any claim that Protestants somehow have continued faithfully in Jesus' and the Apostles' teaching.
So don't crow to long or loudly. If I were you I'd be ashamed, as a Protestant, to pin my case on the existence of "only" 8,000 quarrelling, sniping denominations. I'm deeply ashamed and embarrassed and sorry over the existence of the division between Orthodox and Catholics and the dissent among Catholics. I'd never make it cause for triumphal crowing.
Actually Protestants have as much agreement on fundamental doctrine Salvation, and sin as Catholics do.
Look around your church and see that 50% of Catholics do not go to mass on Sundays, thus rejecting the church rules. Look and see how many have 2 child families and see the rejection of the ban on birth control . I could go on but you know what a cafeteria Catholic is. Every one of them is actually their own denomination .So do not crow too loud :)