@OP: I can understand the player not always wanting to be a rookie in-game, but a combat-hardened professional... but imho he (and to be honest, both you and the new GM too) is kind of handling this wrongly.
400BP characters are NOT fresh-out-of-bootcamp, barely skilled, wet behind the ears, rookie runners.
At least not when built correctly.
But when built the way this guy's made his character, even after 500 karma, half a mil nuyen and limittless availability, he'll still be sub-par.
I don't know how good you, new GM or any other of your players are at building characters, but imho, two steps should be taken:
1. Go over the rules again, show him what John Q Public's stats/skills would be, show him what an average ganger's skills/stats would be, show him what average corpsec would be like.
2. Then ask him what he wants his character to be able to do. (From what he built, the only real thing he's got going for the character is Automatics and several IPs and boosts gained from 'ware, so in short: a Streetsam). Then show him a couple of streetsam builds. You can find plenty of examples around this forum. Watch the 'Runner's Black Book' thread, Umaro's char examples and/or pick a couple of the combat builds in the PbP's OOC threads; there's dozens of builds to pick from.
Each and every one of those builds are not only rules-legal (usually either 400BP or 750 karma), but also a lot more capable than the character he built with trice the amount of resources.
Show him their skills/stats (and compare them to 'normal' people or even 'runners with a different specialization) and he should understand: These may be beginning characters, but they are NOT beginning 'runners. They can take on half a dozen corpsec guards without breaking a sweat... and probably three 'streetsams' the way he built them too.