Intamin really makes some amazing rides, but their biggest successes seem to be very conventional steel coasters.
I mean, no? To me this feels like a case of reverse survivorship bias. Plenty of what you would consider a "very conventional steel coaster" goes back to something that Intamin had put major innovation into. The line between "strange idea" and "bold idea" can be very fine from time to time, and yes, Intamin is much more successful with ride types that we would consider to be conventional these days, I'll give you that.
But I'd like to adress some points on your list.
Reverse Freefall coasters (two built in 1997, never again since)
I'll give you that one, these are basically oversized flatrides and maybe a proof of concept type of work. However, their obsolescence was mainly a result of the invention of the hydraulic launch system, which is an Intamin product as well.
Impulse Coasters (seven built between 1998 and 2003, but for some reason a park in China is building one this year)
Similar case, almost oversized flat-rides. With the vertical spikes, they could be seen as a more compact version of the same idea that is utilized in the accellerator coasters, and their obsolescence mainly comes from Intamin themselves figuring out what to do with launched coasters besides just having a launch.
Suspended coasters (three built between 1998 and 2001)
I mean yeah, not a great one. But also not a novel coaster idea at the time, though that just adds to the confusion rather than helping me defend Intamin.
Plug'n'Play woodies (four built between 2001 and 2008)
The Intamin Woodies had their place in their time. They absolutely **** over any wooden coaster built pre-2001, it's not even close. They are irrelevant now because their price-tag was no longer justified as soon as GCI figured out how to reliably make good wooden rollercoasters the traditional way at a fraction of the cost (which falls around the 2004-2007 era) as well as the end of the coaster wars and the financial crisis in 2008. As soon as the coaster market recovered, there were plenty of more economically viable options on the table, that doesn't make the Plug'n'play Woodie any less of an engineering marvel though.
Aqua Trax (one built in 2003)
Weird idea that found its niché once. Not really a loss as well though, I don't think anyone got excited other this idea like ever.
Half Pipe (four built between 2003 and 2006, one of which never opened)
These are not even somewhat flat-rides, these ARE flat-rides that just utilize coaster track. Why are we talking about this.
ZacSpin (four built between 2007 and 2011)
The S&S free-fly proves that anything that might have been problematic with Intamin's approach to this idea is completely fixable (or even Insane at Gröna Lund for that matter). If it weren't for the ****ty trains on Green Lantern First Flight and all the other annoying stuff that was going wrong with Intamin projects at the time, Six Flags might have bought these in bulk from Intamin and S&S would have never been able to fill in that gap in the market. This model did not fail on itself, it failed because Intamin had too many problems surrounding the time this model came around.
It seems like every few years, they try to reinvent the wheel, have some initial success, and then the models for whatever reason stop selling completely.
I mean yeah, they try a lot of stuff, but it's also completely normal to have the majority of your pilot projects go wrong. Plenty of engineering firms on this planet would kill for Intamin's track record. B&M is trying ****-all because they witnessed how badly ambitious projects can go wrong during their very early years when Arrow Dynamics went bankrupt. Intamin has pioneered the giga coaster and the modern launch coaster, that's like the coaster-engineering-equivalent of inventing Asprin and Penicillin. Or chocolate and Coca Cola, whatever. These are exactly the "conventional large steel coasters" you mentioned. Intamin made these coasters conventional.
Meanwhile B&M and RMC have a near-perfect track record because they have like 3 coaster models. It's their approach to doing coasters. Have one near-perfect track profile that allows you to focus 100% on the layout itself. That's not what Intamin is about though. They casually changed their track-profile for Taron just to make it less view-obstructing for all the scenery around it. Nobody talks about that, yet that sort of thing would be completely unheard of with any other manufacturer on this planet.
tl;dr without all these weird, failed coaster models by Intamin, we wouldn't have all the good stuff as well. There's no need to get excited over everything Intamin does, far from it. But I still get excited over the fact THAT they are still doing stuff.
