Yes, there are regional variants of Modern Standard Mandarin, but the ways in which these deviate from the proscribed standard are predictable and in fact generally internally consistent. Note, this is a separate matter from the dialects themselves, which are usually not mutually intelligible with Mandarin, although they influence the regional character of the Mandarin itself spoken there.

The thing is, subtitles are everywhere in China (Watch any movie or newscast), because it is difficult if not impossible to understand dialect speakers, and beyond that, to understand the non-standard mandarin that has been influenced by the these dialects.

The problem with the sentiment "I can get by just fine without tones"(obvious paraphrase) is that "get by just fine" and "without tones" are both statements that need further qualification.

I maintain my central point: Tones are obviously important in a tonal language, and the extent you can be understood without using them is determined almost entirely by the skill of the listener, as well as their acquaintance with other non-standard speakers and/or foreigners.

The reason for my tone in these posts is that I think this sort of attitude speaks badly for all foreigners studying Chinese. It betrays a sort of borderline arrogant exceptionalism that says "I can learn Your language, but on my terms. And in English, there are no tones". The reality is that Chinese speakers have come to expect very little from foreigners who are studying their language...and ironically this just continues the cycle, and these cocksure foreigners receive affirmation for simple, atonal phrases that native speakers must work hard to understand.