Woah okay I go away for a day and speculation blows up, especially about ride similarities (which is my specialty).
Alright here we go. cracking knuckles
Parks have had a history of adding similar rides to their neighboring competition for a long ass time, hell some are bad enough to where they do it in the same park.
I will keep on bringing up Dorney, GAdv, and Hershey with their habits of playing follow the leader. Batman, Great Bear, Talon. Steel Force, Nitro, Skyrush (and if you want to be a smartass, 2020). You also have SeaWorld San Antonio and Fiesta Texas which both share a goddamn Batman clone in the same Municipality.
As long as there's a gap between the additions and a difference in the product nothing is going to stop a competing park from going "we'll build that." At least with a Star Flyer BGW won't have to keep a set of evacuation cages on hand at all times or have a medical team on standby incase the wind goes above 10 mph because guests will get kneecapped. A Star Flyer can also actually run in a steady wind.
As per its similarities with a Wave Swinger, most of the Six Flags parks got rid of theirs because they were park originals and parts were not easy to come by. A Star Flyer and a Wave Swinger also have similar height restrictions (both of GAdv's are/were 42 inches) which any way you smell it is much more accomodating than Windseeker's utterly asinine 52 inches. North Star at Valleyfair also is proof of concept you don't need a gaudy topping element or some extreme lighting package, so if it's planned for properly it doesn't need to light up anyone's house at night.
So onward and upward to the roller coaster discussion. It was my understanding the original giga concept was going to be more Red Force than traditional. Reuse Drachen Station, launch out towards Festa Field, Top Hat, come back. Nothing exactly world breaking there. It also falls in line with quarterly performances and business strategy that BGW and SEAS thought the money would be better invested going into two separate expansions instead of one gigantic one. B&M was never really on the table for me from the get-go and I doubt there was any behind the table dealmaking going on between the park and manufacturers.
Now going into the competition between BGW and KD, outside of Richmond I think y'all are severely overestimating the clout of their "rivalry" along with why Twisted Timbers came to be. Twisted Timbers fit the bill more as a smaller Gwazi and not a "oh this is definitely a shot at competition." It was the cheapest alternative move comapred to taking it down and replacing it with literally anything else, especially since for whatever reason KD couldn't reopen the ride for 2016 or 2017. KD before then was content with keeping it around because it was out of their way and the capex they were spending was going elsewhere in the park. Which if you ask me even 5 years ago was the smart move. KD needed that appearance update along with all the rides it added in place of Hurler for the 40th anniversary timeframe. That same situation can be brought up for Tornado as well, but the demolition was cheap enough to warrant even with their 2019 capex share they started receiving around that time.
Back to that rivalry though, BGW and KD both are in economically advantageous positions in terms of geographic position but in terms of population they're stuck between a rock and a hard place. Richmond, DC, and Norfolk / Newport News are simply not major population centers like Philly, NYC, and LA, or have the population growth like Charlotte or Phoenix. BGW hit that threshold before Griffon, which was why we all remember that insane marketing strategy they had for 2007 and 2008 advertising all the way up into New York. KD has hit its threshold some time before Intimidator, but it's jard to grasp when due to the administration changes and KD not being one of the top parks in terms of annual attendance, so they don't really get brought up that often along with their numbers. The attendance threshold I am talking about btw is simply the ceiling of what the local population base can do in supporting an amusement park. Almost every mid-major to major amusement park in the US has hit it at this time because people simply are not paying to go on huge trips like pre-financial crisis, so parks are trying to crack that mould by bringing in fresher markets away from Disney and Universal with that carrot of "you don't have to drop a mortgage payment to come visit us instead." This is why you see parks building sporting complexes and hotels, they're building their infrastructure for what will hopefully be another boom like what happened before the financial crisis. BGW already has that infrastructure in place, along with the other major SEAS parks, so it's only natural they drop more money into rides and getting a quicker return on them instead of building up for something that might not even come. KD is in a similar boat with hotel infrastructure around their park, but their issue is that there's nothing to do nearby outside of the annual state fair. There's less of an incentive to visit compared to BGW, Hersheypark, or Dollywood, all of which have their hands in some of that DC / Richmond / Tidewater pie.