We're comparing 5 seeds tracking thousands(?) of full nodes vs 14 Stratum servers... 14 > 5, and 1000 > 14—it's difficult to judge which is more decentralized IMO.
That's a good point, but conversely collusion among Stratum servers, with their small count, is easier (and likewise for dns seed servers).
I think it's too hard a comparison to reach a conclusion of one method being more "secure" than the other. Of course, the factoid doesn't say "more secure", it more carefully uses "perhaps somewhat more secure", so if you still think "or header-only clients" should remain, I'll just drop this