We should still be trying to be realistic, and surely someone who starts today with accumulating $250 per week of bitcoin has a chance to reach 1 BTC in 10 years if they are able to increase their weekly (or otherwise) BTC purchase amounts in the coming 10 years. If they stay at $250 per week and have no other BTC purchases, they might not reach 1 bitcoin in 10 years... So there are needs to try to be realistic within what we are currently capable of doing and what we project ourselves to be capable of in the future, even though the future remains a projection in many ways, so the shorter the period of time, we can attempt to be more realistic with what we are able to do as compared to further out projections having a lot of variables that could end up changing our abilities to buy bitcoin at the same rate or even at a changed rate (whether higher or lower).
I agree with you, we need to be honest about what we want to achieve. Investing $250 every week is good, but if the person have no other way to add more while accumulating, it may be difficult for them to reach 1 BTC in 10 years as the Bitcoin price continues to increase. So we need to plan according to what we can afford right now.
Sometimes we believe we will make more money in the future, but things change, and it is better to focus on what we can do now and to build our holdings little by little. Sometimes life does not go as planned, and the Bitcoin price changes, so we should be ready to deal with anything. And, in my opinion, we should just be consistent, even if the money is not big. the goal is to keep buying what we can afford and not to put ourselves under unnecessary pressure.
It might be very impossible to reach 1 bitcoin in 10 years with weekly buys of $250 worth of bitcoin which would amount to $130,000 in 10 years due to bitcoin progression. In ten years time, it is projected that bitcoin price should be near $500k at least which depending on the level of volatility could rise above $150k before the year runs out.
The most important thing should be maintaining your DCA allocation and keeping to it strictly except in the case of pay raise which you may consider to increase your DCA allocation which would also increase your chances of achieving the 1 bitcoin 10 years projection. Cooperate bodies have upper hands as they can easily acquire this in months. So to this end, it's more advisable to focus on the amount you intend to invest and the period of time you intend to invest such amount (probably 10 years or more) instead of focusing on the amount of bitcoin you wish to acquire which could expose you to investing beyond your capacity when the time frame seems too short to achieve same. What matters more is accumulating continuous and seeing bitcoin rise to where it belongs. Whichever way, you still stand a chance to make profits at them end.