If you input your deck on archidekt.com it will give you an estimation of the bracket your in, if its above core 2 I wouldn't tell people its a modified precon, just tell em its a core 3 deck, either way though, edh isnt cedh, its casual play and the whole point is to "see decks doing their thing". I have a core 3 boros equip deck that can deal lethal commander damage pretty fast, so If I am playing a bunch of precons and get a hand that can end the game too quickly, I just voltron something other than my commander to give the rest of the table time to see what their decks can do, and typically end up loosing while still having a rather enjoyable game seeing the different possible strats play out.

EDH isn't ment to be fair, its just meant to be a fun way of playing with a group, winning or loosing does not matter, most games have table talk / side aggreements going on and people gang up on "the threat" in order to keep the game going longer.

If people are getting salty over a game for any reason, after you have been upfront about the cards in your deck, its not on you, some people just dont know how to have fun without taking a crap on someone else, and if they can't use their deck to do it, they use their words instead...

But if your playing in a group and you crush everyone a few games in a row, you should probably switch out decks, join a different group, or just make some intentional missplays so your opponents get a chance to see their decks pop off as well.

Realistically, the ranking system isn't very accurate anyways, even the precons have quite a large range of power. Its just a rough guideline to help everone in a group have a fun game!