The specialized mining hardware is a red herring.

The security of the Bitcoin network isn't a function of its hashrate or the number of nodes, though these things correlate; it's a function of the cost of running it.

Regardless of whether the network is run on specialized hardware, old desktops, or TI-83s, the network is only secure so long as it costs enough to run that any motivated attacker would have to spend more money than they can leverage to attack it.