A few questions

[jiji]

Apologies if any of these are easily answered by referring to the books.

How do clerics get new rituals in their ritual book?
Why does a human bandit L2 minion get attack +6 vs AC
and a L2 human bandit skirmisher only get +4
(I'm assuming +2 prof, +1 Str, +1 from level)?
Why do some Str modifier stats in the MM take account of the level of the creature and some appear not to?
Do high-level wizard spells really do less damage than L1 warlock spells like Flame of Ph?

 

[TimeOut]

How do clerics get new rituals in their ritual book?

Buying them, or by finding another ritual book.

Why does a human bandit L2 minion get attack +6 vs AC
and a L2 human bandit skirmisher only get +4
(I'm assuming +2 prof, +1 Str, +1 from level)?
Why do some Str modifier stats in the MM take account of the level of the creature and some appear not to?

Monsters are mostly designed according to guidelines. These are no fixed rules. If you want your Str 25 monster to hit for 1d4 +1, it is totally possible.

Do high-level wizard spells really do less damage than L1 warlock spells like Flame of Ph?

A warlock is a striker, a wizard is a controller. Yes, the warlock powers should deal more damage, while the wizard spells should control areas.