We'll see fees move high & low but they'll have to go down or else it's going to be expensive sending micro payments. There's cheaper options to save fees but you'll want to hold your bitcoin if you can.
I don't think fees will go down to a point where you can use BTC for micropayments. It will only be feasible through "The Lightning Network".
For now true but who knows what may happen in the nearest future in bitcoin technology and how advanced it would be, if bitcoin would ever achieve what satoshi envisioned it to which a electronic p2p means of exchange without trusted parties or middle men, bitcoin right now is more like an investment asset and serves better for such purpose, many would not even like to store value in it cause its still quite volatile, I don't ever think in the perspective of bitcoin replacing fait but in the future we might have many means of exchange and bitcoin could be one of them even if not with the lowest gas fees but maybe more affordable, like bringing it to a lowest minimum of 1 dollar or maybe cents.
Scalability would not always be a problem for bitcoin, much can happen in years to come, no one really knows what to expect.
While I don't recommend unnecessarily leaving funds on exchanges, you're option here is to not withdraw the BTC after every DCA purchase. Instead, probably do the withdrawals biweekly/monthly(whichever you're comfortable with). That way, you'll significantly decrease your fee payments.
This is the obvious answer.
People should not leave their bitcoin on an exchange to sit for a long time because there is always the possibility of the exchange getting hacked at some point. And in general you should be in control of your bitcoin since Bitcoin allows you this ability. But leaving coins on an exchange for a matter of weeks or a few months is extremely low risk if you are using a reputable exchange. If the ratio of your fee-to-DCA is high enough that you are complaining about it you should just move your coins off the exchange less often. Problem solved. Also that way you use a bit less block space and make the blockchain ever so slightly cheaper for everyone else.
There really is no reason to move off-exchange every single time if you are DCA'ing. Assuming you're not using some shady exchange, which would be a much more serious problem, just do it once a month or once every couple months instead of every week.
Always use common sense. Don't just blindly follow rules people say. Yes you should control your bitcoin yourself, but that doesn't mean you can never make use of an exchange's custody services. If you're literally hurting your finances just to follow a rule of thumb then you are doing things wrong.
Just like you're not going to buy a $5 coffee using an on-chain transaction paying a $3 fee, you're gonna use the LN and pay a <1 cent fee, you shouldn't be making an on-chain tx for every single DCA if you're only DCA'ing like $50 or something at a time.
Your quite right, just keep your bitcoin or holdings on reputable exchanges like binance untill you have accumulated quite enough for up to 3 months then move to your hard wallet or any self custodian means you chose.
I myself I normally don't do a lot of transactions with crypto except my weekly DCA which could max up to 100$ at times and 20$ at times, so I just keep my holdings on the exchange untill it's up to 500$, then I move it to my ledger hard wallet, safe and easy.
But remember not to store or hold on exchanges, not advisable, potential hack may occur and you have just lost your holdings.