In my opinion, the only suicide lead set that warrants deletion is Forretress's.
WreckDra stated correctly that it has no discernible niche in this metagame and is severely outlcassed. The other 4 all have unique niches and deserve analyses (except for maybe Greninja). In order of viability, I would rank them Cloyster > Excadrill >> Scolipede > Greninja, with a noticeable gap between the first and latter two.
Cloyster and Exca both mandate similar amounts of support from their team, namely solid Darkrai anti-leads. They're relatively consistent vs every archetype and synergize well with a myriad of potential of anti-Darkrai mons. Leading something like MMY or MGar vs sample HO is justifiable when using them because they can just spin away any hazards Deo-S sets. Spin also opens up Ho-Oh as a potential teammate for handling Darkrai. Both obviously deserve analyses.
Scolipede is one of the few viable anti-leads that effectively deals with Deo-S and Darkrai. This alone grants it a niche in the metagame. Being deadweight vs magic bouncers, MGar, and Mence is really shitty, but it's the best anti-sample team mon out there. imo, it's much easier to make a team good vs bulky stuff than offense in this metagame (just make Dialga the SR setter; also fixes the Mence problem) and Scolipede is one of the fews mons that excels at this.
Greninja's niche is beating both magic bouncers (Modest Hydro 2HKOS MSab). However, it requires the same team support as Cloyster and Exca, but doesn't provide the benefit of anti-leading Deo-S, which is why I can rarely, if ever, can justify using it. Using Greninja mandates Diancie as its team's mega in order not to auto-lose vs the sample HO, which really kills a lot of potential options for support (fitting an offensive spinblocker, fastmon, ekiller check is tough w/o the mega slot on these teams). By far the worst suicide lead because it's dead weight where you need it the most.