I disagree.
You might be thinking of it in terms of "well, they'll make up the difference with just one year of PS+, then the rest is gravy."
But that only makes sense if you assume that every single sale is going to someone who wouldn't have bought at $299. That is patently false, considering Sony continues to sell hundreds of thousands of units each month at $349 (unless you take the position that without going to $249 their sales will crater and/or by going to $299 their sales will triple vs what they would otherwise). For every sale you're getting that you wouldn't have otherwise at $299, you're giving an unnecessary $50 discount to 1-2 other people.
If they're going to $249, it's to step on MS' neck in an attempt to drive them out of the console space.
Upping PS+ is just grabbing profits, in a manner similar to what MS did with locking Netflix, etc behind Gold.