@1
Two forms of interaction are certainly not necessary against combo (countering being the superior one because it prevents topdecking into outs and turn-1-kills otd). In fact a deck like Shardless BUG is so mediocre against combo (though it has FoW and Discard) that it started splashing white JUST to have Meddling Mage for the combo matchups.
Xantid Swarm is pretty garbage against my 4 Bolts and 2 Golgari Charms. Speaking of storms you pretend like Storm never beats a Thoughtseize. When they have (put) a Tutor on top it can happen that they just laught at you getting one of their 3 rituals/artifacts, going for Past in Flames/Ad Nauseam next turn.
Also Discard doesn't prevent your opponent from topdecking an enabler for his combo. It's kinda like BUG plays against the opponent's hand, RUG is playing against the whole deck. The disadvantage RUG has here is that they don't know about their opponent's hand, but they already have topdecks covered in their head because they already account for these cards. And often times, you just have to play to your outs and it's enough.
I'm also not saying that RUG is superior as it has certain weaknesses like Carpet of Flowers or a quick Empty the Warrens (reason why I like Golgari Charm), I'm just pointing out the strengths that imo get often times neglected when comparing these decks' plans.

@2 Yes, because I waited longer with Brainstorm, I'm in a better position. The reason for that is that often times you can pretty much divide your deck into lands/creatures/combo-hate when you look at it. It's vital to have the lands and creatures at the start, but the longer the game goes ("long" meaning past turn 2) the less you want lands and (more) creatures. You have to filter really hard to actually get to combo-hate*.
With BUG you often have to Brainstorm if you have (almost) no action in hand, digging less deep (trying to find discard-sorceries). When you keep Brainstorm up for the worst-case and are able to cast it perhaps several turns later because the opponent DIDN'T go off this turn you had nothing in hand, you get rewarded by being able to shuffle away more "garbage" that got stuck in your hand.

@3
My creatures might be smaller, but my Delver flips slightly more often and I have Bolts so it should be kinda even. Which Combo-decks play REB? Painter and Show&Tell? Well, against Show&Tell I have my own REBs so it kinda evens out, right? And against Painter thanks to my own REBs I can destroy Bloodmoon when they go off and stop them, so it doesn't seem that bad. REB seems pretty good against combo that play it themselves imo.
To the Show&Tell Matchup: It's one of the best for RUG because they have to fight over a single expensive spell (at least cmc3) which is just awesome when you rely on stifling their mana, spell piercing and dazing them. Thoughtseize is pretty good here as I know, but Hymn e.g. is sometimes just bad when you're unlucky. Relying on it sometimes just costs you the game and is really bad when they e.g. Pondered or Brainstormed, leaving an important spell on top.

*It's irrelevant here if that's a Thoughtseize or a Spell Snare here (your example of spell pierce which is rather bad against Storm is better against Show&Tell), Combo loses to a hand full of counters as well as to a bunch of discard with counter backup if played correctly. Even without Gitaxian Probe I can tell how to play (sometimes to my outs) a lot by which cards I have in my hand.