This is one thing where I think Paizo actually *almost* did something cool; the advancement rates could be scaled to Slow/Medium/Fast. If 5e adopted something like that to the system, I could live with that. Each class could then be given a base "adjustment" (e.g., thieves might get +5% xp, barbarians might get -15%, etc.). Then the DM could choose S/M/F for how quickly he wants his game to progress, level-wise. Each class could then still be "campaign balance" oriented and not "class balance" oriented.
I don't get the point of +5% or -15% or whatever for individual classes. My last campaign lasted almost three years, but there were a few PC deaths, players leaving the campaign, new players joining, at least one left for over a year and came back for a couple of sessions, etc. Different XP values is just adding complexity for no reason.
That said, yeah, I totally get the "modern life" thing. I'm constantly both annoyed and flabberghasted by some of my co-workers and people I talk with who can *not* have quiet/silence in their lives for more than 3 minutes or they start to wig-out. Patience, as a virtue, has gotten beaten, starved, kicked and all but destroyed in todays "modern life". So, yeah, I get it. I don't like it, but I get it. Luckily enough for me, I am a pretty patient guy...so I can just sit there and watch the ensuing trainwreck when the power goes out and my co-workers start to (literally) loose it if the power stays off for more than 10 minutes. Quite facinating, actually...in a perverse sort of "watch them suffer" kind of way... >
That's not what I mean. My games run 5-6 hours on a weekend night. It is not easy to get someone to commit to that time, as we're all adults, in the 25-40 range. Some of us have to commute for more than an hour from out of town, not me though. (There is literally one married player in the group, and we play at his place. Not surprisingly, he's not DMing.)
The issue isn't today's shorter attention spans at all. I know the internet is shortening my attention span, I can still play a 6 hour game of D&D. I don't bring electronic devices to the table unless I'm DMing, and I don't even have internet on my laptop.
PS: IIRC, ol' EGG suggested that a normally run campaign (6hrs/week) with a group of 5 or 6 players should have characters hit level 9 in a year
The only reason my campaign lasted that long is because I'm a glutton for between-sessions work. In my current group we've only had one other campaign last that long. Even then, neither long-running DM normally runs every week, and four weeks between sessions of an individual campaign is typical. If we used the 1e-style advancement rates, we'd still be level 7.
I don't think it's a good idea to have a class that is weak at level 1, then expect the player to hang around for months until they're no longer weak.
I don't want to say anything "bad" about EGG, but he wrote that game decades ago. I played it in high school as well and could level up quite quickly. I'm not back at high school anymore.