i even won 89 and 94 with such a squad! -- self-irony aside, my first thought at seeing that team went along the lines of "how can this possibly cover brave birds and especially staraptor2 (which outruns even 252+ spd pheromosa) any better than my setup?" -- i suspect that another very good reason for using toxapex, mega-slowbro, mega-mence, mega-scizor, aegislash and chansey is their ability to sponge most neutral hits on at least one side of the spectrum, since very few configurations pre-bank that cover all the types are viable. sure, guzzlord goes well with aegislash typewise, but it appears to have wailord-like base stats and
always gets hit before it can do anything, whereas hydreigon doesn't deal enough with a scarf (252 satk modest surf does not even ohko 0 hp / 0 sdef salazzle) and doesn't run fast enough without it. and as you've said, even "bulky offense" with good weakness coverage, which is what i like to think i have tried so far (kartana/specs tapu-fini/sash garchomp), simply cannot afford repeated switches -- when you check a type, you must outspeed and knock out the quarry afterwards, or at least tank whatever coverage it can fire at you (prime examples from my experience so far: flash cannon heatran, life orb infernape).
e.g. whenever i ran into lead sunnybeamers (say arcanine or typhlosion), the correct tactic was to switch to tapu-fini, tanking flamethrower, then use surf on the predictable sunny day for 40% damage (foepas berry), then switch back to kartana on the solarbeam, as despite its poor special bulk, it can take them rather comfortably. then sacred sword delivers the knock-out and a beast boost, what's not to like?
but then you come across e.g. lead staraptor, for which one set runs choice band close combat (ohko on kartana) and another runs z-brave bird (ohko on tapu), not even to speak of the choice scarf set. with the team i've been using, i find myself unable by design to make an informed decision against this opponent. there is no way to know the set before you essentially risk a coinflip (actually the switch to tapu is favorable 75%--25% when all four sets come into question, because 3 out of 4 staraptor sets will not 2hko, but imagine using a 75% accurate move for super singles; and i think certain trainers only use sets 3/4 which really would render this a coinflip -- note that i'm not too acquainted with those mechanics yet and have avoided looking at TRE's list for a while, because i have strange ideas about fun). and you never want to gamble in the tree. in contrast, when your switch-in is mega-slowbro or aegislash, you hardly care about whether you're switching into brave bird or close combat.
and this is a huge element to why defense wins more reliably: you are not only less prone to misprediction, but also to situations in which you need to cover all the possible sets of a pokemon. staraptor would never be a problem if the game just told me the set before it could make a move.
i have been thinking about whether the intel gained from abilities such as frisk or (only if abilites are) trace could justify the use of e.g. porygon2, or mega-gardevoir postbank (if we get the stone at all, fingers crossed) for bulky offense edit: just remembered that abilities aren't fixed (most amusing: protean greninja with spikes and toxic orb effect spore breloom), so trace gives no such advantage, but maybe we have an argument in favour of eggy-alola here, haha
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Yilx: iirc you can get one free focus sash from a dancer on the beach of poni wilds, who battles you with a team of four oricorio, all of them sashed (maybe you have to defeat all the trainers in the area first) -- i guess you have one now, though, but perhaps someone else reading the thread will find this helpful
