I have seen preflop solutions on sites like range convertor that don't have flatting ranges unless you're in the BTN or BB. Is this how we should be playing?

Does this change if we are super deep?

Also, why is it bad to have flatting ranges from these other positions?

In games without rake, or at least those that charge based on time, there seems to be more flats in other positions. One reason to 3b/f in positions where we're not last to act either post or pre (BTN/BB) is the immediate advantage of scooping without more money getting taken out. Mainly though, it's because we're extremely vulnerable to squeezes. By overcalling, we incentivize others to 3b more since there's more to win immediately, especially since the overcaller(s) cap themselves.

The more your opponents know about the game, the worse it is to have flatting ranges from those positions. A live 1/2 game likely has the worst players imaginable, so overcalls are much less likely to get punished. If you're playing 1/2 online or higher where the pool is tough, it's probably best to only flat out of the BTN and BB pre.

It's not bad theoretically much less in practice

Reasons against flatting:
-Pay more rake
-Vulnerable to squeezes
-Capped range can be punished

Reasons to flat:
-Realize equity with more hands
-It's free real estate if you're not being punished

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So theoretically there are flats from almost every position vs RFI. SB flats, BTN flats, CO flats, etc. However, as you get more and more players behind you, you need a stronger and stronger flatting range. At a certain point, most of your hands would rather 3bet than call, so it becomes pragmatic to switch to a raise/fold strategy.

At online lowstakes your flats will get anhiliated by the rake. In high stakes the rake goes down, so you can develop flatting ranges. In tournaments you see a lot more of this, as flatting vs an open becomes more common than raising the open in a lot of spots. This is due to the ante and lack of rake.

Besides rake, you also want to pay attention to the openraise size. The smaller the raise, the better your odds and the more you can flat. Against an EP minraise for example, it's quite important for SB/CO to have a flatting range. Whereas against a 3x open it's perfectly fine to play 3b or fold.

Another factor is the raiser's cbet frequency on the flop. The more often he cbets, the less hands you want to flat preflop. Whereas if he is cbetting too infrequently, it allows you to flat more hands, since all the borderline hands in your range will realise more equity postflop.