Clarification on the role of the Marksman in a team comp

So it seems to be a pretty common opinion on these boards that towers are wet cardboard, easily destroyed with relatively low damage. I'll take that at face value: there are certainly more tools to siege towers it would seem than a few seasons ago, and I'd bet mages having reasonable tower damaging autos helps that a fair bit, as a mage mid can actually take a tower solo eventually, which didn't feel like the case once upon a time.

So here's where I get confused: I also hear frequently that marksmen are necessary in any team comp because they have the ability to kill towers safely at range. Without a marksman, you'll never break the siege. And yet, with tools like baron, rift herald, or even just a support sufficiently equipped to shield/heal/protect the damage, and with towers being wet cardboard, you'd not need an adc to burn through towers, or any objective really, so long as your replacement option had steady consistent dps, and the team has the ability to destroy towers at reasonable speed.

I ask this question because I've noticed that, particularly when I'm not behind by mid game, my damage to objectives while playing Trundle surpasses that of my adc. Obviously I don't use that as evidence of the viability of melees siege ability, particularly given my elo, but it did prompt some of these game theory questions, if that helps explain where I'm coming from.

So I guess my question to these boards, and any theory crafters out there, is twofold: are adcs still mandatory for their ability to siege towers, and if you were to play a game without any champ tagged with the marksman role, how would you go about filling the gap?

I'll start the ball rolling with my 2 cents, though I play entirely too casually for my opinion to be in depth. I would suggest that ADCs are no longer picked for their ability to take objectives quickly and effectively, but rather for their exceptional teamfight, synergy with support itemization and kits, and safety throughout the game allowing them to scale into late game more reliably than, say, a mage or bruiser. If I were playing a game mode free of marksmen, I would look first to consistent sources of moderately ranged ability dps (EX: ). Failing that, I would look to fill in with high damage (slow moving) melee champs that scale well with damage stats ( ) and look to a more engage oriented support, or rely on a tank jungle/top initiating. This would correct for any loss of damage, and hopefully without an adc on the enemy team and some engage oriented supports they wouldn't be kited into oblivion, but I'm frankly not sure if it'd be enough.

Would love to hear Gameplay's thoughts on the matter! Cheers!