I am probably going to come across as a grumpy grognard
That won't exactly make you stand out, here. ;P
but I'm feeling a bit miffed about the lack of single-session or "mini-series" games in modern Dungeons & Dragons.
True, the published WotC offerings are hardback APs. But AL had plenty of 'Expeditions,' I think it was, modules that were playable one-off.
I got nolstalgic. Then DnD 5e came out and it was awesome, so I bought it and started building my own world. My campaign has been running for over two years now.
Welcome back.
What happened to the old tournament games?
They were replaced by the 'Living City' campaigns, culminating LFR which was abandoned by WotC c2010, IIRC. The RPGA was folded into the Wizards Play Network, and while it might technically still exist in some form, replaced by AL with the release of 5e.
So, really, AL /is/ the modern equivalent of the old tournaments.
I'm not sure, because I only run AL so have never tried to invoke it, but I believe you do get credit for running, so can play a higher-than-first-level PC if you've been running games for a while, and, (again, not sure) if your character doesn't use anything specific to a given AP, you can play it a bit here and there and level it up over time.
I know that at Conventions you can find DMs running games like this but I've had bad experiences.
Well, some things never change. ;(
Really looking for opportunities to play the occasional 6-8 hour one-off session with a mid-to-high level pregens. DnD Encounters seems to be designed for the exact opposite experience.
The 6-8 hr game seems almost a thing of the past. Blame it on the short attention spans of 'kids these days.' ;P And the limited time available to working adults.
Likewise, high-level play has gotten something of a bad rap this millennium. (And, if we're being fair, it was never something that worked wonderfully well - it could be fun, but it got crazy and 'broken.')
It does indeed seem to be a fairly modern assumption that every adventure has to be part of some overarching campaign
I blame Babylon 5 and LOST.
Part of it might also be an increase in the complexity of character design. It took a hell of a lot more time and thought to understand a pre-gen 3.X or 4e character than it did in earlier editions. 5e definitely seems to be the better option but there's still a proliferation of class abilities (thanks to the "no dead levels" design philosophy).
There are a lot more options than there used to be, yes. (In 4e an off-line CB character sheet could be pretty easy to take in, if you could get past the instinctive distaste for pages of M:tG-like 'cards.') In 3.x or 5e, the complexity of a higher level pregen will mostly be in the spell list, if you're very familiar with spells, no problem, if not, madness - you won't even be able to decide what to prep. The solution, IMHO, is to use classes like the Sorcerer or to present the pregen with spells already prepped. And to have the complete texts of the spells known or prepped readily available (even printed out with the sheet, or, ironically, in the form of spell cards).