We are not "one" airline per say.
We are both an International Airline, and a Domestic Airline ie.. WB vs NB
Then you have to look at Line Holder vs. Reserve... they are 2 different beasts!
Lastly, you have to look at where you will be living, ie.. are you planning on being a commuter vs. living in base.
THAT will really determine what kind of QoL you will have.

Lets be honest, 2 yr upgrades at ANY major/legacy in not the norm. And it will go away at some point. Same with WB newhire positions.
There is a reason why these things are happening. It's great that "new" Pilots are in the drivers seat about where they want to go. But just remember, it can all stop in a heartbeat.
9/11 showed us that. Then the Global Recession in 09.
If Putin pulls a tactical nuke out of his pocket, all bets are off again!

Back to your question-
777/787 Line Holder as a newhire. Um.. YEARS!
756 Lineholder as a newhire. Anywhere from months to years based on where you are Based.
The movement from Reserve to Lineholder seems to be at the NB (73[GUPPY]/Bus). If you believe what management has been saying, they "want" to replace a majority of RJ flying with mainline. That's great! But with that comes RJ type flying.. expect 3+ legs a day and 3 or 4 day trips.
The devil is in the details. Many don't know that the company is allowed to 'Mini Pack' you as your last leg gets delayed, before another trip the next day! Allowed per the UPA.

Good Luck no matter what you decide
Always
Motch