I decided to make a separate post about this because I'm not asking for an online mode within this system as it is, I'm suggesting a new idea that should (in theory) prevent the devs from having to do a lot of work to make any sort of offline play work. I read posts about this from over the years, many reasons as to why it should happen and why it won't work.
For reasons why, a post was made just a week ago providing reasons (that are somewhat obvious haha)

Here's an idea for the offline version

A separate executable+shortcut that uses the same resources but stores the information on a separate local file. So this version would only include the "custom match," "story mode," "Training," and "Heroes" tab, I guess. All things using bots and AI that don't require multiplayer. This is the main thing people want, I think. And it should (in theory) be more doable than an 'offline mode' since it would be a separate executable that would not mess with the current server systems that require internet to begin with.

Other Aspects -
The game would save on a local file and be separate from multi player, but maybe some people wouldn't want to do X or Y all over again. Having an option to download game-save data from online servers (this ironically would require a connection/log in, but only once) would address this perfectly and would perfectly suit players who are, for example, leaving home (and going somewhere without internet connection) for the holidays but would still like to play as their characters and train whatever they've already unlocked.

Business
I'm not exactly sure how having an exact copy of the single player portions of the game would be 'bad,' but if the devs would like to incentivize the online version, I think it would be understandable to limit some aspects of this version, such as certain executions, appearance customization or something that's more cosmetic. I honestly feel like it would receive a lot of backlash, but it would be understandable enough to live with. Also if it cost 5 - 10 extra USD to unlock, I'd pay up. More than that would be too much imo haha, but the option there in the first place is most important