We aren't sure they won't be any good without them in the new codex.
Even if their stats and cost are exactly the same, that doesn't mean they won't be good. For one, we won't know how the whole thing works together until we get a chance to play it.
If some of the rumors hold true (e.g. points reductions across the board, more ways to provide threat saturation, long range firepower, good fliers, etc.), I don't think an enemy can really worry about wasting it's very few S8+ weapons on a Warrior brood when a Flyrant, 2 Haruspex, a Trygon Prime, a brood of Carnifex, and 3 Crones are coming at them. All while a Tervigon is pooping Termagants all over the objectives, mind you.
We can't just compare units in a vacuum. There's way more to this game, and Tyranids in particular, than that. Synergy, the mission, the opponent, and everything else in the list will matter. The 5th edition book sucked because it only had about 2-3 cost effective units, and the Hive Tyrant was only added to that mix because of the BRB psychic powers. A remotely threatening unit like Warriors appeared and naturally they were going to get shot.
Now Tyranids will have more viable options and build styles, and the sweet spot for weapons is S6 & 7, not S8+. If an opponent wants to waste -- er, use his/her 200 point Riptide on my 170 point brood of Warriors, be my guest. It'll be fun watching literally any of my Tyranid MC's take it out next turn.
Warriors will be good if players figure out how to use them, not ONLY because of Eternal Warrior, T5, or some ridiculous save. It's like people want GW to tell them what's good instead of figuring out how best to use what they have. Anyone remember the Eldar release? Everyone said the book would be bad because Runes changed. Now how do they look? People said the Helldrake was too expensive. Now there are 3 on every table. People literally said, "I don't think you'd ever want to field a Riptide. For the points it doesn't do enough." Now people cram as many in as possible.
The initial observations are correct right around 0% of the time. I expect that trend to continue. One needs to play about 30 games at different points levels, against different opponents, and with different mixes of units before an assessment can even be considered.