Noted~ModNote: Please keep discussion focussed on the Metagame we're developing for, rather than a non-existant CAP Doubles format which we do not build for. Cheers :-)
Slow Start is certainly a monumental factor in its poor performance, but other factors include the following.
- A milquetoast typing that offers nothing offensively and but one immunity defensively.
- A complete absence of recovery apart from Rest.
- A feeble base SpA with no reliable STAB, meaning it cannot run a mixed set.
- No setup options other than Rock Polish.
- A fairly standard array of utility options (e.g. Thunder Wave, Knock Off) that encourage it to bounce rather than realize its potential.
So directly looking into theses specific aspects, almost in a way that involves fixing Regigigas as ways to circumvent or neutralising the effect of Slow Start, the CAP would either:
a) Rely on bulk/recovery to gain enormous set-up advantages for a Dracovish-level Sweep after 5 turns.
b) Serve a stall-based role similar to Toxipex with decent Sp.Atk to cover for the lack of Atk at the start.
Out of those two: option b) is the most interesting for me, since it allows more interaction during the Slow Start turns.
A existing mon that is around about those lines is Kartana: Attack 181, Speed 109, with a BST of 570. Now a large portion of Kartanas strength came from Beast Boost upping it's Attack with every KO, and I would believe that were Beast Boost changed with even a neutral ability, Kartanas power would drop. Slow Start would be killer.Something like 170 base attack and speed on a relatively fragile mon with common enough checks. Starts ok, but if it keeps making ground and forcing the opponent out or killing them, it turns into a monster.
Following with kj's point: standard practice with Kartana was maxing its Attack and Speed EV's, resulting in a final of 507 and 348 respectively. (depending on nature). Slow Start would therefore put those stats to 253 and 174 when initially sent out, roughly equivalent to a mon with Base 60 Attack and 30 Speed with the same EV and Nature bonuses. Kartana was barely kept in check with it's almost non-existent Health and Sp.Def; I genuinely don't think it's possible to have that type of stat-spread on an non-legendary BST and be expected to last even 1 turn, yet alone 5.
My mind immediately goes to a defensive Pivot in the realm of Assault Vest Magearna but for Physical Attackers.Speaking of Give and Take abilities, the one ability from that category that I wouldn't mind seeing is Perish Body. It's the only ability from that category that doesn't have any real positives, but it still has some potential that I think we could really bring out.