What exactly are you trying to trap with magnezone that can't be taken out with the 4 guys with fire/fighting attacks? If it's heatran(probably not but you never know sometimes) I'd replace close combat on mega pinsir w/ earthquake which also hits megagross harder.
Toxic spikes is too slow on an offensive team like this, nothing can stall out enough turns to do substantial damage plus vs stall, mega sabeleye is a pain and you won't be able to rapid spin away the rocks that hurts megapinsir x4, talonflame x4, weavile x2, talonflame is your win con vs stall so removing rocks is really important against them, therefore I'd recommend a defog user like latios, the scarf set outspeeds and revenge kills lopunny(megapinsir's quick attack deals with loppunny tho) or it can potentially lure heatran with a life orb/expert belt and kill it with EQ so talonflame can brave bird people in the face. If you don't like Latios, excadrill is also a good choice, sableye is still going to be a problem but scarf moldbreaker excadrill can surprise kill Rotom-w who otherwise walls birdspam, sooooo many people forget he has moldbreaker and switch in rotom-w when they predict the scarf set.
Next instead of heracross I would recommend Clefable. The standard calm mind and flamethrower/fire blast set is my favorite but people have seen success with unaware sets with heal bell and such, it can also run stealth rocks, I always make it mandatory to have a clefable on all my teams because I hate stall so much, you could also opt to run a manaphy with tail glow and 3 attacks(make sure one of them is energy ball for slowbro).
After that there's 3 ice weaknesses, 3 fire, 3 rock, apart from being a frail niche revenge killer I don't think weavile contributes much apart from removing landorus.megagross, which it can only do if it gets a free switch in, which will be when one of your pokemon dies. Plus it cannot OHKO megagross which sometimes carries bullet punch.
There's a couple of choices for replacing magnezone and/or weavile (until I hear your reasoning for magnezone, just dawned on me that skarmory could prove to be a problem unless you hit it with Talonflame).
Rotom-W: will-o-wisp is awesome,Opposing talonflame can outspeed mega pinsir @+2 and OHKO it, Hippowdon has also become quite popular recently, resists fire and ice, slow volt-switch to give your 2 set-up sweepers a free switch in(do not megaevolve pinsir if you know your opponent has something like landorus, pinsir has hyper cutter and can live a stone edge, granting you a free swords dance) and is generally just an amazing pivot in general
Dugtrio: Kind of strange but hear me out, the most common pokemon that can stop talonflame is heatran, w/ heatran gone most teams don't have another check to BOTH mega pinsir AND talonflame. Scarf Tyranitar can also be very scaldy, pursuit trapping latios and potentially OHKO'ing both pinsir and talon, plus potentially removing mega manetric(assuming no rocks) is always a plus.
Heatran: Heatran is very versatile and can fulfil a lot of roles, earth power can take out opposing heatrans, magma storm can trap and destroy stall and grab you switch advantage. It can set up rocks or even run a scarf set. The main reason you'd be using him is for pivoting into the likes Charizard Y, Charizard X lacking earthquake, talonflame, latios,scizor, clefable, ferrothorn, and mainly rotom-w who's going to either will-o-wisp or volt switch most of the time. Plus mega pinsir can easily switch into fighting types and earthquakes aimed at heatran often granting a free turn of set up. Heatran also deals with skarmory freeing up a slot on your team.
banded/scarfed reckless staraptor: Often a double-edged sword but back in BW2 hyper offensive teams generally ran 5 similar sweepers with similar counters because a balanced/stall team generally only has 1 or 2 answers to them. Having 3 birdspammers is kind of the same principal but generally it'd be a better idea to balance out your team and focus on getting the sweep with either talong or pinsir.
Finally grass types like poison heal breloom or tangrowth almost solely for dealing with rotom-w, landorus and hippowdon, they can also potential take out tyranitar. ferrothorn is another option if you'd like to set up rocks but can struggle to hurt landorus at all. Scarf variants will not appreciate u-turning into iron barbs/rocky helmet and will be less inclined to do so coupled with rocks. Tangrowth can also run knock off and can even take a lot of damage from most pokemon w/assault vest except from the likes of Charizard Y's sun boosted fire blast but random stuff like life orb starmie only 3HKO with ice beam only the likes of Kyurem can score a 2HKO with ice beam so it can easily tank hp ice coverage in a pinch.
Generally your game plan should be to remove/weaken your opponents checks/counters to pinsir and/or talonflame, stealth rocks is a game loss unless you remove it. Having a pivot like heatran/rotom/ferrothorn is essential to keep your loses to a minimum instead of sacking a pokemon everytime. You can never have too many outs to heatran and rotom-w, generally being sneaky with latios or natural gift talonflame is the easiest way to do it. Hippowdon may not see a lot of usage but it can shut your team down if you can't answer it. diancie could also be a huge pain. The best way to structure your team is Pinsir +talon(swords dance is the best IMO but there's also taunt/bulk up for stall/balance or choice band for raw power and weakening counters/checks for pinsir) plus non-flying type defog user or a rapid spinner that can reliably beat sableye(you could get away with most spinners if you run magic guard clefable to check sableye) Then add a pivot and two mons to help cover as many threats to your win con as possible though exceptions can be made for the likes of dugtrio. Heatran and rotom-w being the most commonly seen but in general most electric types(manetric, thundurus even Zapdos or raikou), physical defensive walls (skarm, hippowdon,slowbro) and faster threats or pokemon that resist your flying type priority(diancie, tyranitar, heatan, megagross(rock polish can wreck)
