The 50/50 assumes youre adding your willpower. Otherwise with just the commlink, youd get crushed...
Crushed you say?
Attacker would roll Cybercombat + Logic [Attack] which for argument sake is 6+6 dice
A 345k deck have the limit array of 4, 5, 6 ,7 (so the current limit might be as low as 4 or as high as 7 - depending on how much Firewall, Data Processing and Sleaze he want right now).
Defense roll is Intuition + Firewall [+Willpower if you use Full Matrix Defense]. No limit.
Firewall 6 is just 5k away and since Intuition is used for Initiative even the street sam might have an intuition of... say 4? Without slaving the stuff to another member in the team and without using Full Matrix Defense you would still have 10 dice.
12 dice [5] vs 10 dice. You cause matrix unresisted damage to the cyberdeck on tie or win.
That is pretty good odds for not having to spend even a free action to fight back. About 50-50 i'd say.
If you spend some initiative on the interrupt action (yes interrupt, you can take it at any time - even not during your own action phase - and it last for a full combat turn) you even get to add Willpower to the defense roll. More dice than the attacker. No limit. Win on tie.
And, let us not forget that you are still just a free action away to turn off wireless which make you immune to Matrix Attacks. Not like your equipment is
useless[ without the wireless bonus... shrug.
...and if the decker does fill your entire matrix condition monitor on your device before you switch to local mode (which in this example would take about 2-5 complex actions), you still only need a simple tooklit, 1 hour and 1 single hit on a Hardware + Logic [Mental] test (or a Logic + Logic - 1 [Mental] if you don't have Hardware skill) to fix it enough to restore
full functionality in your device again.
Now - put the decker in line of sight of the street sam and see who wins that fight

Spiders are not rare, but remember that the vast majority of them are Riggers; Controlling building security, cameras, doors, jumping into remote turrets, coordinating living patrols, providing intel, calling for backup etc.
Security
Deckers are pretty rare (information wants to be free etc - crazy hackers).
As a Street Sam I would be more concerned about fighting spirits without help from a Magician than fighting a security rigger without help from a Decker.... Shrug.