mastercomsI don't think there is a valid argument for keeping them different, but hopefully recontextualizing the debate into two sections: should they be different, and then if not, should we use the stock or IB hitbox, will produce better discussion.
That's fair. I'd like to talk a little bit about why I think an increase in direct pipe radius is good for the game, and I also think there's a broader lesson about the evolution of games and metagames to be gleaned from this discussion, using the overall change in demo pipes as a lesson. Here are two thing that I'm not sure everyone knows/remembers:
1) the iron bomber, while having a larger projectile hitbox than stock pipes, has a smaller blast radius (at least according to the weapon description)
2) the demo nerf of 2014 didn't just nerf stickies, it also nerfed the blast radius of pipes by reducing them to the same as rockets
What do these two facts mean? Well, Valve clearly intended demoman to be a defensive, zoning, artillery based class, and the stock pipes of the time reflected that. Old pipes would hit someone and splash anyone even remotely in the same zip code (as would stickies), and the relative unpredictability of rollers would further punish teams that were clumped too much together. On the flip side, demos could be vulnerable if you closed the distance (especially back then before so many pipe savants existed), and thus Valve figured that their glass cannon, area denial class was balanced.
However, the developer's intentions don't always square with the realities of the ever-changing metagame. It may seem obvious now, but when players discovered the power of the left-click-right-click, the ability for demoman to impact the game as the aggressor in fights went massively up. Couple that with pipes that could splash wide radii, and rollers that could det perfectly on retreating players, and a demoman exhibiting well-timed aggression could sway a fight almost single-handedly. Of course, we play with demo limit 1 for a reason, which somewhat balanced things, but it was still pretty clear that demoman was the most powerful combat class in the game. It was still god-tier at what Valve had originally intended its purpose to be, but it was good at so many other things as well, and was just completely centralizing the meta.
However, when Valve decided to nerf the class, and to buff scout a couple of years later, the balance of power massively shifted. With the reduced blast radius of stickies in general, and quick-fired airstickies in particular, it became much more difficult to reliably lock down an entire zone of the map, allowed scouts in particular to move wherever they please (because they are lower hp than soldiers and don't have the tool of the rocket jump to circumvent a particular area entirely). Coupled with the med movement buff, scouts became what demo was a few years prior- still the best class at cleanup and selecting its own targets, as well as less interesting things like capping, but now the best direct offensive class in the game as well with its ability to chase (and arguably the best defensive class with its ability to give meds easier ability to dodge damage). Of course, that's not even to mention the fact that scout limit is still two, and that the medic's ability to keep up with scouts, coupled with the demo's reduced ability to deny an entire area has made double scouts near the med in dry fights much more powerful. There are lots of consequences to this meta that I don't love (like the loss in specialization between pocket and roamer, positional play of meds becoming too forgiving, the utter mindlessness of the double combo scout strat on mid or dry fights, etc.), but that's for a different time.
Still, tf2 players are adaptable, and eventually demos realized that, to have a larger impact on their game, they had to focus more on single-target dmg. That's not to say spamming an entire team has no purpose or anything, but a demo's ability to precisely hit charge stickies or direct pipes on a single target became more necessary, particularly when those targets are either scouts or feeding soldiers (now that both soldiers are freed up to play roamer a decent percentage of the time).
This is where we come back to the iron bomber- with its larger hitbox and smaller radius, not to mention more 'direct' but also more predictable rollers, its purpose seems tailor-made for the new way of playing demoman- it may not be as good as old stock pipes at killing 4 people at once in badlands choke, but it's a hell of a lot better at directing a lone scout on the top of process mid. To me, this represents a positive overall shift in the metagame- demoman might be EVEN FURTHER from what valve intended it to be, with greater 1v1 ability, but it still fits a specific niche- the best midrange class in the game, with the lack of damage falloff, that can still be vulnerable at extreme close range but only in the form of soft counters.
To be clear, I'm not saying Valve intended any of this; they might not even realize the iron bomber hitbox is so different, and if they do I'm sure they think pubbers are too dumb to notice so they don't have to update the stock pipes. However, this point doesn't matter to me- lots of the best metas that develop in games are not intended by developers, and may even come from bugs originally (see: all of SSBM). I also highly doubt Valve intended scout to be so strong, because I'm sure they were doing the demo nerf more to appease engies who like to build giant sentry nests on badwater than to appease 6s players.
Now, if we somehow got to go to a pre-demo nerf and pre-scout speed time, then yeah, the direct pipe upgrade (or maybe just the rise of better pipe aimers- remember, a metagame can change despite ZERO actual changes to the game itself) would be too broken, because the demo would just go back to having almost no weaknesses. However, I'd say that scout today doesn't have strong enough weaknesses, and a demo with really good pipe aim is one of the few things keeping them in check. We may have even entered an era where the soft counter rock-paper-scissors is reversed. Years ago, it was somewhat accepted that scout soft countered demo, which soft countered soldier, which soft countered scout. This made sense when demos were worse at defending themselves directly, and when soldiers had a) more heals than scouts and b) a shotgun (not to mention scouts having worse movement, and the map pool having more badlands/granary style maps). Now, it seems like almost the opposite- gunboats soldiers, freed up from as many med responsibilities, can land on demos ad infinitum, while 185 scouts can kite them endlessly, and demos can kill a scout from any distance beyond close range more efficiently than a soldier can. To see scouts whining about iron bomber pipes, therefore, seems pretty myopic to me.
I realize that this is the biggest tl;dr in a thread full of tl;drs but what can I say I love theorycrafting.