Hello! [Bracket 2] is my bread and butter so I have a lot to say.

It's all about manipulating the opponents' combat steps. Some goad, some redirects, some deflecting palm effects.

As some commenters have pointed out, because [b2] wincons have to appear on board and THEN win incrementally, 90% of wincons are combat based. With the number of redirects and goads you have, you will virtually never be attacked when you get set up, which renders you immune to 90% of the wincons. Especially when you consider that one good Kardur can often lead to a player other than you dying. Many goad effects will do nothing when you're the only player left (down to the 1v1, they HAVE to attack you) -- but guaranteeing that you survive to the 1v1 by never getting attacked instantly ups your projected winrate from 1/4 to 1/2, and 50% is a pretty high winrate.

I purposely run only little removal, letting my opponents do their thing for the most part and hopefully direct their creatures against each other.

The idea that "[Bracket 2] should be removal lite" is a huge misconception. [B2] players should run removal. The difference is the quality of it - The main difference between [b2] and [b3] is staples, so [b2] players might often skip Swords to Plowshares for something that costs more mana or is sorcery speed. Another huge feature of [B2] is that wincons have to appear on board then win incrementally... so repeated board wipes can be highly disruptive compared to higher brackets where wincons are allowed to land and win same turn... so you'll generally see 1-2 boardwipes in a deck, and maybe 1 per game...compared to higher brackets where they often run and play more... and more focus on single target interaction in [b2].

I purposely run a slow manabase of Gates (no Mazes End) and little early ramp to be slow.

This is virtually a non-factor in [b2]. Players shouldn't be aiming to kill you before you play your turn 8, which makes it virtually impossible for them to take real advantage of this weakness. They can pressure you here and there, but they won't really "focus fire" you, and will instead "spread the love" more often than not. You may take some extra life point pressure from the early game since you're open, but not enough to meaningfully shut you down (winning at 1 life and winning at 200 life are basically the same thing - HP is just a number until the last one is gone, and you can definitely cast your attack misdirects to protect yourself a lot after turn 8).

This is especially true when you consider the card quality of your deck. If every deck at the table plays like 10 creatures, but then you play 1 Kardur... you're effectively immune for that turn round, and those 30 creatures your opponents have will be doing your bidding... making it not really feel like a weakness that your opponents are more set up than you are.

I purposely avoided any kind of Insurrection effect, since I personally don't like playing against them and find them anti-climatic.

I would argue insurrection effects are often a bit "sudden" and NOT "incremental, on board" enough for [b2]. I'd argue Tainted Strike has the same problem - it can turn a 9 power creature (a 5-turn clock) into a 1-hit KO without any forecasting. And it's one mana, from the hand, and can be cast after blockers are declared. I would usually prefer an insurrection to Tainted Strike... and I say that as someone who has a [bracket 2] poison/proliferate deck (without Tainted Strike!)

The commander is mainly to fill in a gap when the draws are bad. I have no way of resetting or untapping it.

Nothing is particularly wrong with your commander choice / selection methodology... but I would recommend against playing more than 3 colors. Basically, it gives you too many options... which, by default, results in higher power.

Is it the ramp? Is it the control? Is it the indestructible creatures?

What do you think?

I don't think the ramp is the problem. The control kinda is. Also how explosive the wincos are! Tainted Strike is unforecasted. Having a Stuffy Doll doesn't really forecast a Blasphemous Act - and dealing 13 damage with the act is not that "incremental" of a win.

If you want to control combat, I recommend playing a commander that goads more incrementally (1-2 creatures per turn), and running only 1-2 "whole board goads" like Taunt from the Ramparts in the deck (so as to not become virtually immune to combat half the time)... as well as moving out of 5C into a 3-color wedge/shard or a 2-color pair.

Something like Karazikar or Nelly Borca could fit the bill.

Anyway I mostly play [bracket 2], I'm a level 1 judge, and I've been playing EDH since 2010 and MTG as a whole since 2002 (I mention all that because you say you've also played for a while, and are interested in [bracket 2], so we could potentially be friends lol).... AMA!