I will try to address your points as best as I cam 
Defense - yes a properly equipped decker will far outshine someone with just a commlink for matrix defense .. so without a decker (or TM) on your side you will be leaving yourself pretty vulnerable to being hacked ... that leaves how you equip yourself as being the limiter on how detrimental that is
To infer: The other tech archetype (Rigger) has to rely on Deckers or TMs for defense of his kit?
Wireless - wireless bonuses are still a thing and will probably be just as impactful if you are paranoid about being hacked ... most of the bonuses feed into the action economy (effectively making certain minor actions a "free" action by giving you a bonus minor action ... ie changing a clip with a smartgun"
Wireless bonuses were a mixed bag of good and garbage* in 5e and I am disappointed to see that they are maintained. Wired and wireless should be primarily be a flavor decision.
*Examples of garbage:
- Smartguns connect to the internet to improve real time ballistics? Nope. Weather.com isn't going to help your math.
- Stun batons charging makes them hackable? Nope. They are charging from the presence of wireless, not the exchange of data. Their wireless bonuses do not make them hackable.
- The internal router and anything. My cyberware already has a DNI per the rules and anything that a DNI shouldn't be covering, this shouldn't cover either. This is a missed opportunity to macro multiple cyberware actions.
The survival knife is a good example of wireless bonuses that make sense.
Usage - this is more of a misconception I think... you can (and could in 5E) still access a device in your possession without connecting to the matrix just like in today's world your typical smartphone has a limited amount of functionality even with no signal but connecting to the matrix increases that functionality exponentially. There are no specific rules that state how useful something is without a matrix connection one way or another and should be handled with common sense.
A better example is a smartphone and a laptop. I can share my internet connection with my laptop via USB or WiFi hotspot.
In SR, if I connect via USB, it's not wireless so I don't get bonuses for being online. I can't get my Windows Updates. I can't stream my movies from Netflix or Prime.
If I connect via Mobile Hotspot. Suddenly, I am "SR" online and can be hacked from a block away.
If I'm connected via a LAN to a T1 line, it's the same "not wireless" nonsense.
It's dumb. Anything that requires a connection to a remote server should work whether there are a wires involved or not.
How MAD are deckers - well that will ultimately come down to play style but for 95% of what a decker is intended to do you only need 2 attributes and 2 skills
How about a tangent from a point above?
How MAD are riggers - Is it an equivalent investment to decker(s)?
How easy is it to fill multiple roles? - In general, but also specifically, how easily is it for a character to be a decker and rigger out of the gate versus how easy is it for a character to be a Technomancer and a rigger out of the gate?