Of course, if it is possible to hold Bitcoin in the long term, then such investment strategies must be adopted. Investments are usually only profitable if they are long-term, but investing with a small amount of money can be done long-term only by following the DCA method.
Buddy you might be having some misconceptions about investment but investments are not "only" profitable in long term, short term investments too are profitable but you can't obviously look into that as an option in bitcoin because we consider with as wagering or gambling but which is more important to shitcoiners because they can't obviously hold those coins for long term.
when we say long term, we should be able to state out what we mean by long term and extablish the reason why we're considering investing for the long term. We've used the term long term investment so much that a lot of people are begining to assume that once you've invested for the long term you're bent on being profitable with your investment. In reality, it's not how long one holds his Bitcoin that matters, for as long as you care, you can choose to HODL $500 worth of Bitcoin for 20 years and look at it as a long term holding and won't be half as profitable as one that holds $20k worth of Bitcoin in less than 5 years. While talking about long term investment it's best we also relate it to the essence of making the investment for the long term. If you're just investing for the long term and you're careless with how much you're able to accumulate within such timeframe, then your long term investment wouldn't make any difference.
Building a portfolio with a long term plan in mind gives you an opportunity to to build a resource that guarantees long term investment and when you have a good plan in place and follow it out to the latter, it's going to make a huge difference in terms of how much you're able to build your portfolio at such period of time.
People often think of investing in wrong kind of ways.. like you mentioned.. investing $500 or even $5k and then just sitting on it, when more likely there could be something like $500 per year (which is ONLY $10 per week) or maybe $5k per year, which would be $100 per week, and so maybe after several years, there might be a determination that enough money is in the investment, so then there is no need to add more to the investment, yet making those determinations regarding how much is enough are going to be somewhat personal.. and so if you have a cash flow, then you can keep adding, but then there might be some point to add the money to some other asset with the determination that there is enough bitcoin, but then the bitcoin portion might not be ready for cashing out.. so there could well be 4-10 years or longer between the time of putting the money in (accumulating) before there might be some desire to start to withdraw from the investment - whether the withdrawals might be price based and/or time based, it hardly makes any sense to me that the withdrawals would be all of it at once or even large portions at once, so there might be thoughts of the withdrawal process being long term just as the accumulation and maintenance period each were long term.... ..
and as we know, this thread is not so much about the next stages of our investment journey, but instead about how to build up our BTC holdings to get to those further stages and to have more options after having had spent years building up the BTC holdings...and most are going to need several years to build up rather than just throwing in some amount and sitting on it (even though surely there are some folks who invest in lump sums and then just sit on the investment, even though the trade offs for that style could well be regretful in terms of not being able to turn back the clock later down the road when we are better able to see what we did as compared to what we should have had done.