You don't need to combine the lump sum method and the DCA method if you are not strong enough or have the capacity to do that because you can end up making a mistake or run out of discretionary income though combining the two will boost your investment and make you get to your set target quick but you need to have what it takes to carry out this because lump summing required a large and huge discretionary. Any method you use to invest in Bitcoin will give you a reasonable value provided you are doing it well or properly.
There's no big deal to lump sum provided that your DCA is ongoing and it isn't even a most to lump sum whenever you don't have thw funds to lump sum. You are making lump sum look like it's only for the rich or that any investor on his ongoing DCA accumulation journey shouldn't lump sum because they need huge discretionary income.
You might have a discretionary income of $50 out of a weekly pay of $200 and you are using part of the $50 to DCA. That doesn't mean that if you are lucky to be paid double salary or you were given funds as gift in an occasion or bonus and you never expected it or have serious pressing needs that you will use the money for. You can just buy bitcoin with it right away. It's not compulsory that you must always have such an amount all the time but once in a while is cool.
It's only not proper to depend only on lump sum accumulation of bitcoin to build your portfolio. That is where the problem of waiting or large amount of money to lump sum wouldn't speed up the growth of your bitcoin portfolio.