This is going to be long so sit back and put your feet up. There are so many factors at work in determining performance in skiing that to focus exclusively, or even predominately, on one is a mistake.
What you appear to be asking is: Will increasing my body mass improve my results? You might consider instead, asking where can gain the most in my skiing performance?
XC skiers at the World Cup level demonstrate one of the widest variations in body types of any endurance sport. One can examine the relationship between results and any number of physical or physiological metrics. Over the years many such correlation have been done to try to find meaningful relationships that might help coaches produce more successful athletes. I can tell you that absolute body mass has little to no relationship to performance. In approximate order or importance here are things that appear to correlate best with performance: #1 with a correlation upwards of 90% is the Speed you can sustain at lactate Lactate (or anaerobic threshold) , #2 with correlation also north of 85% is Economy (distance covered/energy cost) which is integral with #1, Trailing these by some distance and only explaining about 70% of the results difference is #3 Aerobic Power (measured in oxygen consumed/body mass/minute).
Body weight does not correlate well with race results. Likewise, absolute strength does not correlate well with skiing performance. If either of these did, then weight lifters would dominate the WC.
Instead, power to weight ratio plays a roll in sports like XC skiing and mountain running. But not in the way you might be thinking. Maximum power (such as max power on a C2 ski ergometer) or by extension, maximum strength (such as dead lift) do not correlate well with ski results. Thats because XC skiing is an endurance sport where the ability to sustain high power outputs rules the day. A 2km (around 6-8 minutes) uphill double pole test correlates very strongly with performance because this tests the percentage of that maximum power you can sustain.
So adding muscle mass MAY improve your performance if you have been especially weak but at some point packing on extra pounds will start to harm your performance. You have to carry that added weight up the hills. In a race you spend roughly three times as long going up hills than you do going down them. In a race this means that being even 2% slower on the uphills due to the added mass will translate in to many more seconds than being 2% slower on the downhills.
You demonstrate more than adequate basic strength if you can do pull ups with 160% of body weight! That’s super impressive for your age. That is already in the range of US male World Cup skiers like Simi Hamilton, Andy Newell, Torin Koos with whom I have some personal experience. At issue though is how well do you transfer that basic and non ski-specific strength to your double poling or V2. The reason is that the rate of force application in a weighted pull up is far, far away from the rate of force application in similar ski motions like double pole or V2. Raw or dumb strength must be coordinated by the brain to produce powerful and economical sport movements. So getting strong for strength’s sake is a mistake. Just as is adding weight for weight’s sake.
In my 40 years of ski racing and ski coaching from young juniors, to master age class, right up to Olympic level I can say that most skiers (and especially masters) will be best served by improving economy in their skiing. At your age you can not improve your maxVO2. As you’ve seen, the gains you make improving basic strength will be good at first but they will plateau and may even slow you. However I have repeatedly seen double digit percentage gains in actual ski performance such as speed at anaerobic threshold (even with several WC skiers I have coached) when economy is improved. This is some low hanging fruit for most skiers but often overlooked in training programs because it is not so easy to coach and the satisfaction of doing more L4 intervals or lifting heavier weights is very seductive compared to often frustrating and slow gains made with technique work.
It is hard to improve the things you already do best and easiest to improve the things you are worst at. Focus on where you stand a chance to make the biggest gains.