Finally! A claim of backwards compatibility that I can't argue against!
Indeed.
I don't think it really matters. There are far too many variables with 4 specific classes and subclasses to account for balance, let alone all the classes and subclasses.
No, there aren't. Classes are not that diverse, not are subclasses. People like to
believe that D&D is some utterly unpredictable, beyond-constraint creative wonderland where even the tiniest claims will never be useful. That belief has always been balderdash.
There are,
even in 5e where balance has been treated with extremely cavalier attitudes, clear and consistent patterns. Moreover, there's plenty of math you can do which helps tell you the
general shape of the data. The
whole point of statistics, as a formal science, is to take things that seem like they must have too many variables...and then reveal that actually it can all be
reasonably accounted for with just a little bit of effort.
The only way these claims hold is if you demand absolute perfect uniformity. No one demands that. Hence, it is a straw man argument: you are setting up an easily-defeated argument that
no one actually defends.
Party make-up, feat choices, spell choices, stat choices, etc. will all affect how capable a party is.
But all of these things are actually quite constrained,
especially in 5e where the numbers are smaller. It is quite possible to do useful statistics that can produce
actual predictions. They won't apply to 100% of tables. But if they apply to >95%, who cares if they're wrong <5% of the time?
You can't make a monster that accounts for anywhere near all of that in order to challenge them near equally.
Absolutely correct, because you are applying a far, far too stringent standard: "near equally." That is a demand for things being effectively perfect.
Nothing statistical is that good. But it is
quite easy to do statistics that give you a 95% confidence interval for how challenging a creature should be, given the spread of options. That interval won't remain perfectly constant, as the game grows, but there are steps you can take to avoid it becoming totally useless.
This "just give up, there's no hope" attitude sets the perfect as the enemy of the good, and then uses that to declare that we should never bother in the first place. You'll never be da Vinci, so don't bother picking up the sketchbook. It's an absolutely infuriating self fulfilling prophecy: don't try because it won't work, oh look they didn't try and it didn't work!