In theory yes!! That's generally how it works - The buy back is not what I remember on that though because I think it used to be at 10? ((Also I have no idea why I added the +2 SYN to each ally - I think that was at a time where I was overtuning that MEC because some folks were complaining Melee builds were too weak so I had to shuffle a whole bunch of stuff down to give Martial Artist slightly more kit))
I might tune it down slightly (or more likely cap that DMG at 15 or something - Direct DMG in general needs another balance pass since its sources are so varied) - But the idea is it's a more or less guaranteed one-hit against non-boss enemies ((in general non-boss enemies are meant to go down very fast, usually within the first attack or two of getting hit - Something I'm trying to emphasize better in 0.14))
The draw back on Roundhouse is meant to be that it's a bit pricey to buy back and that you don't generate SYN for others ((again why I'm puzzled that I ever added the +2 SYN to allies)).
Re; it being on a Starter Part - Players can (and will as I've both seen and done) build a lot of very strong combos out of that list because they're all balanced to be taken to the end of the game.
That said Roundhouse will probably be getting a minor nerf ((In one of the campaigns I'd played in it was my staple part for obvious reasons but even then it got a minor nerf of only having one charge + at the time it generated no SYN which is a v bog part of how that part works // pseudo balances itself))