The past 2 days have given us the returns of the Undertaker, the Rock, HBK, Edge & Ric Flair (via HOF) and now.. Brock Lesnar to WWE TV. But really when you look back at the past year, you'll see the returns of Kane, Booker T, Kevin Nash, Mick Foley, Chris Jericho, Steve Austin, and Bret Hart (sprinkle in the sporadic appearances of Hot Rod, DDP, Goldust, etc) just to name a few.
Now couple all this with the usual staples; Cena, Orton, HHH, Sheamus, Punk, Show, Henry, Khali.. in conjunction with the talent that's "right there" closing in on Top-Spot status.. ie; Cody Rhodes, Daniel Bryan, Kofi Kingston, Wade Barrett, Zach Ryder, Dolph Ziggler, Alberto Del`Rio, Jack Swagger, Miz, R-Truth, Santino Marella, Ted DiBiase Jr. and probably a few others I'm forgetting. (not to mention the rumored returns of Rey Mysterio & Batista)
..is this the deepest WWE roster we've ever seen? 
This is a really generous post.
No, its not the deepest. The deepest would be when Austin, Rock, HHH, Taker, the 3 tag teams (E&C, Hardyz, Dudleys), and Jericho were all at the top of their game and there all the time. I'd say around late 98-02. HHH was literally the best heel in the business at that time. Those guys could run the show and no one would've cared if they didnt get to see Scotty 2 Hotty. What I see now are 2-3 regulars (Cena, Punk, and Orton) who can sell out a building by themselves in certain locations. One of those 3 is a guy that the majority of the male fanbase hates. One is what I would call a "niche" superstar (Punk) who isn't universally popular, and the other (Orton) is a guy who probably would barely get out of the midcard in the late 90s. The rest of the roster I see as capable hands for the most part, but no one would care if any of them weren't on TV the next week. What we have now (besides the established guys) is a bunch of "superstars" who fill a role. There are no breakout stars that can be seen on the horizon at this moment.
Right now reminds me of WWE circa 95-98. Right before Attitude really broke. That doesn't mean we're going to get another break out like that, but it reminds me of the business. Arguably 96-98 the main WWE guys were HBK and Bret, and to a lesser extent, Kevin Nash as Diesel. None of those guys amounted to much of anything outside of wrestling and WWE was essentially in the pits.
As for your original point, I'd say that right now from top to bottom in terms of just in-ring talent is at a high, but deepest ever? Man, there was a time when places like Georgia Championship Wrestling and mid-80s WWF had a plethora of guys that are current hall of famers all over the roster in every level of the card. I think there is a limitation in naming now "deepest". They have a bunch of good utility players, but not the guy thats going to regularly put butts in the seats/pop a buyrate unless they bring back a guy (i.e. Rock) who has proven capable of doing it.
I also would say that I think the WWE has their heads up their asses in certain respects, but the WWE needs stars. They need them bad if their stock situation is any indication. Thats why Lesnar and Rock are being brought in.
