The change will affect nothing in your gameplay. The RoD will have its usage with no changes other than a countdown that shouldn't matter due to the fact that the RoD isn't used to dodge many attacks to begin with. If you heavily rely on it, that's gonna be tough until you make the new item, but for a majority of players, this doesn't change anything.
I don't take it as Fabsol promoting anything or attempting to increase the chances people will craft this new implemented upgrade. I see this change as Fabsol taking modding the game to a new level in which he can change core values of the game in order to meld it more with what Calamity adds. Calamity becomes not just "additional content" but an entirely new way to experience Terraria altogether, with different balancing, AI changes and modifications to way certain items work.
In relation to Vanilla, I see how your argument makes sense. It is a little weird, and I remember pointing out to my friend on Discord that the change initially frustrated me, but then I looked at it in terms of what Fabsol is doing with the mod and it made more sense. He's not just trying to say "Oh, this CALAMITY item is better than that VANILLA item and doesn't have the 10 second timer, looks like you're gonna have to use MY item now! " Instead, he's made sure there's a natural progression and actual incentive to even bother getting the new item beyond "oh I don't need an active slot anymore." Personally I'd get too used to using the RoD as is and wouldn't use the new one at all, but now there's a reason to, and there's no real problem with that.
He isn't sullying what made the RoD great or anything, he's just taking measures to make sure there's a reason to get a better one that ultimately adds a new layer of intricacy to how you control your character in the game.
Besides, like I said: this RoD nerf isn't going to affect your gameplay unless you outright rely on the RoD for dodging on a level beyond "when I clearly won't make it without it."
And I insist, the new item's advantages were good enough to actually do that without nerfing the RoD. It may not come as what I said to you, and that's fine, it's just my opinion. But that's how it felt too me. I'm not complaining about the gameplay, I mostly use the RoD as a comodity item, instead of applying to combat, so yeah, for me it won't affect nothing. Literally.
I didn't really even use the RoD at all to be honest, so maybe I don't have the same perspective as those who DO use it, but I can see Fabsol's reasoning for this quite well. Since this mod is meant to add a crap ton of content, why not encourage people to use the items it provides?
The thing is, the normally relocator (I think that's the name) already has several advantages over the RoD to justify the use. For one, it doesn't affect the Counter Scarf, unlike the RoD, which increase the cd of the scarf if you are on chaos state, or chaos state's cd increases a lot if the scarf is on cd. Also, unlike the chaos state of the RoD, the chaos state of the new item doesn't increase the damage you suffer by 50% in revengeance. Nerfing the RoD was unneeded at this point, in my opinion.