1. 6S-4H 10-15 HCP
2. 4S-6H 10-15 HCP
3. 4S-5H 11-15 HCP (Flannery)
When partner has nothing (or not enough) to push for game, it still becomes a part-score battle. In 2/3 of these hand patterns you end up in 3 of a major. How bad is that compared to a 2NT overcall promising 5-5 in the minors and 5-10 HCP? You end up on level 3 (often doubled) with less HCP. What makes the 2NT overcall A HUGE GAIN FOR THE OPPONENTS is this: you have just succeeded in telling them the hand layout and HCP distribution. They can now bid a thin game in the majors, finessing partner for the major suits.
My 5-10 HCP hands guarantee a 5-card major. When the major is ♠, I can still push the opponents out of their comfort zone into level 3.
When I show 5-5 in the minors 11-13 HCP, partner at least has something to work with now. At favourable vulnerability, 4mX down 1 obviously scores better than the opponents making 3M.
Your 2D bid is fatally flawed by an incredible common hand type. What is advancer supposed to do with a poor hand with 3-3 in the majors? I'd rather play 6-3 fits than 4-3 fits. The problem is even worse with 2-2 (and maybe even 3-2). And don't say you pull 2H to 2S with the 6S4H hands, why would you want to push it up a level for no reason when advancer is 4-0 in the suits. The problem is exasperated when the opponents compete further. Say partner bids your 2D and RHO bids 2NT lebensohl (most good pairs won't play double=diamonds), what do you do with 3-3 in the suits? If you pass, what do you do if 3C is passed around to you? If you want a full hand, I'll give you AQx xxx Axxxx xx.
If you double with the above hand (and have it defined as no preference), then you have no way of penalising since the 2D bidder will never double.
While 2NT for the minors tells the opponents a lot, it also tells partner the same information, and can make a proper decision most of the time. Your perception of people bidding 2NT with both minors is that they all have fused dynamite belts attached to them. I'd like to think even the most aggressive bidders would know to stay out of the way with x xx Qxxxx Kxxxx, at least if vulnerable.
Long story short, you can take your -100s, I'll take my +110s.