So first of all, Probopass doesn't really attack. It just sets up SR, uses a status move, and if it's lucky it'll Volt Switch out.
If you really want to use Probopass as an attacker, then special attacking is better. Its strongest physical move is Iron Head at base power 80 (why have you given it Magnet Bomb?), which is the same as Flash Cannon.
Also, Probopass really only needs 1 of each STAB, and its movepool delivers: Flash Cannon & Power Gem. You don't even need to breed Flash Cannon, it's learnt by TM. It even learns Dazzling Gleam, Earth Power, Volt Switch and Thunderbolt all either by level up or TM. You don't even need the hassle of tutoring or breeding viable moves onto it.
Considering how many physical Rock attackers there are out there (basically everything except Aurorus, Cradily, Lunatone, Diance, Corsola and Omastar out of 57 rock type Pokemon), is it really so undesirable that Probopass has better sp. atk?
Also, Steel moves have always been shoddy. There are 19 steel type moves, 5 of which are status, and of the attacking ones there are only 2 moves at bp 100+, Iron Tail (rubbish accuracy) & Doom Desire (very exclusive). Probopass is lucky it even gets Flash Cannon.
So really, don't complain. You don't even need to get another Probopass, just slap some TMs on it. If this is in-game, then there's even less to worry about? You can go through the game with any set as long as you train. Or just... get a Pokemon who's only use isn't tanking.