Yes, it really does. There's absolutely no point in double upgrade. If going from his current cpu to 9th gen, better to bite the bullet and go all out, or not at all. There's very few mobo's really capable of exploiting the 9900k, the rest either don't have the VRM's to handle it, or the EPS power necessary. 9700k, fine, no worries, but 9900k is one of those cpus you need to consider from the start. It's not part of any upgrade path unless planned for in advance with both mobo and psu.
And as far as gaming goes, unless you have both the gpu and monitor to exploit them, there's no point in going beyond a 9600k, which puts the 9400f/9500f as best options for mid range cards, budget gpus and a 60Hz monitor at 1080p.