Yoda's internal monologue in the Revenge of the Sith novelisation is especially telling. In short, as leader of the Jedi (for the best part of a thousand years) he's been assiduously training young Jedi to re-fight the last war. That means an over-emphasis on lightsaber fighting and a dramatic under-reliance on things that might have actually helped them; winning the hearts and minds of the populace and engaging in espionage that might help to root out any dark side users of the Force.
He’d never had it. He had lost before he started.
He had lost before he was born.
The Sith had changed. The Sith had grown, had adapted, had invested a
thousand years’ intensive study into every aspect of not only the
Force but Jedi lore itself, in preparation for exactly this day. The
Sith had remade themselves.
They had become new. While the Jedi- The Jedi had spent that same
millennium training to refight the last war.
The new Sith could not be destroyed with a lightsaber; they could not
be burned away by any torch of the Force. The brighter his light, the
darker their shadow. How could one win a war against the dark, when
war itself had become the dark’s own weapon?
Star Wars Episode III: Revenge of the Sith - Official novelisation
To put it another way, Yoda was expecting the Sith (or whoever) to turn up like this
rather than like this
And encouraged training that would suit this kind of fight.
As to the question of blaster deflection, this is something that the Jedi do deal with in their early training. We see younglings practicing with the same sort of remote that Obi-Wan had Luke swinging at.
Various articles about lightsaber training (including the excellent Fightsaber) address the fact that while many Jedi are happy to deflect blaster bolts (using a modified form III), relatively few were willing to take this to the next level with Form V (deflecting bolts back on those who had fired) for ethical reasons. A fully trained Jedi might still be ill-equipped to deal with the sort of threat that dozens of well-trained and blaster-equipped soldiers would pose.