it was to show that it ISN'T infinitely spammable and increasing mana costs does nothing. You'd either rework to not work on a charge system anymore, or you'd just increase the cooldown if you think a trap recharges so fast to not notice it's even a charge system that you need to save up. Preventing her from using the ability a lot in a quick burst is again going against INTENDED use, which is what the "kassadin treatment" is.
Also it does matter (that her traps aren't truly spammable) because it makes her team more vulnerable to flanks from tp/initiators from the jungle
(really any sort of hard engage) when her team tries to siege. (if she chooses to place a bunch of traps to siege, and your tank like poppy or reksai try to sandwich them caitlyn can't suddenly move away from the turret and place a whole new wall; she'd have to fight in tower range to even use the traps zoning potential, but more likely back away from your turret to not get caught)
Even if they knew they were being flanked and changed their positioning she can't immediately set up traps around the new position. Getting that to happen makes her significantly less effective in influencing fights.
For your scenario the most likely and hilarious thing that would actually happen is that
would kill all of the minions until the enemy team realized that a straight on siege would not even work (in other words before caitlyn could even place traps under your tower).
In the event of a baron siege poppy could ult minions and or champions away to either stall (if some of her team was dead) or flank with reksai and try to catch one of their carries (if poppy's ult again were to create a numbers advantage, even with baron the enemy team would have to respect this if the gold was ANYWHERE near close).
Again the only thing cait will influence here on even grounds is that running straight at the enemy team while your tower is being sieged is not the best plan.
In lane it works the same way. Moving where the fight is often much more possibly than you'd realize. If a cait drops a bunch of traps at once you might think it's still imperative to not get pushed closer to your tower, but she just used the traps and won't have them immediately ready to place under your tower (which is the biggest source of frustration). Also depending on jungle pressure hard shoving the waves after she places traps makes it harder for her to do anything back because she has weaker wave clear now.
In short playing around what she wants to do is going to work poorly. Not letting her play her game is going to work better.
That's Caitlyn in general, and people may get mad saying "wow you have to do all of that do counter her!" well not really because having wave clear, and having hard engage is important with dealing with any siege and is what most people are going to have on any balanced composition. All I said is how to use what you should already have anyway(in other words counter play), but people will just blindly run forward and get mad when they do exactly what cait counters.
As far as any significant changes should go it should either be targeted at a legitimate frustration such as placing traps under enemy towers, or a power shift onto two different abilities.
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her q which has no significant use outside of early game wave clear.
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her ult which is terrible outside of situations where everybody on the enemy team is squishy and has no heals or shields that just negate it completely.
If these abilities were more powerful it wouldn't justify her traps being so powerful. Remember that her traps were said to be a large part of her identity to begin with, so just being mad at them in general does no more than complaining how much most ranged characters hate
windwall.