Is it a waste of time

NO! It's not a waste of time.

Newbie gains are gains made in strength and in muscle. They can be pretty significant.

I have been lifting for about 10 weeks and my body looks really different. Other people are noticing it.. I am noticing it.. etc.

The only thing you WONT do eating at a deficit is gain muscle mass, you will gain strength though and the shedding of BF% you will be doing will make your muscles more prominent and visible. You will maintain the lean muscle mass you do have while losing more actual fat.

Trying to add strength on a calorie deficit. Aside from increasing muscle memory, really how much strength can be gained without eating at a surplus? When people talk about newbie gains, what is considered a newbie and how significant can those gains be? I am at the point of considering I might have to for the first time in forever deliberately eat at a (guessing moderate and predominantly protein??) surplus if I am wanting to gain good strength for my swimming.

It depends how de-conditioned you were when you started. If you had low nuero-muscular efficiency, you could see large increases in strength without any muscle mass increase. It all depends on what you were doing before you started lifting, I guess. You should be able to squeeze out quite a lot though.

Some things that may help:

1) Increase your cals nearer to your TDEE without going above it. Say 200 under. Then try 150. Then 100. You need to fuel your body to make adaptions. Not enough fuel puts too much stress on your system.

2) Make sure you get enough sleep! It's probably the single most important thing. You CNS will not adapt as quickly and as well as it might without quality slumber.

3) Make sure you are getting adequate recovery between workouts. This is when adaption occurs. More workouts don't equal better gains in strength. In fact, quite the reverse. Overwork can actually make you weaker.

Obviously, these are just general guidelines/observations. You don't really list any details about your current routine/TDEE (and how far you are eating under it)/exercise history/etc so it's hard to be specific......

If it makes a difference I am 42, 164cm and about 48kg, think about 21%bf (that was taken when I was 50kg). Swim about 10km a week and lift x3 with the odd run or other cardio.

Cross-post!

You might find that you are trying to do too many competing activities (or at too high a level) at once. Many in season athletes won't lift three times a week, they'll do 2 sessions at most and spend the rest of their time on their sport.

You have a couple of options:

1) get on a routine that has a 2 weekly lifting schedule. Continue with all other activities

2) taper back on the swimming and running and keep the lifting frequency the same.

3) Keep the swimming and lifting and drop anything else.

4) Keep everything and try to eat over your TDEE. You'll probably gain some fat along with some muscle. I don't know how acceptable this is to you. It depends on how much you value your sport.

It's so hard to lose weight and build muscle at the same time it just seems more worthwhile to me to do them separately, rather than trying to do them together and not losing weight as effectively or gain muscle as effectively.

I think she's trying to build strength not muscle.....

Muscle strength and muscle mass are two different things. You can achieve substantial gains in muscle strength on a calorie deficit.

^^^^This. When I started lifting, I could barely lift much weight. After 3 months, I had doubled all my weights and stalled. This was on machines. I stopped for 6 months. Then I started back up with barbell compound lifts 2 months ago. Strength has again increased significantly over that time and I have been in a deficit the whole time. By significant, I mean: squat - 160 lbs to 215 lbs, deadlift - 205 lbs to 315 lbs. Bench is stalled due to a shoulder injury. That is all gained without adding any muscle mass (I do regular BodPod visits to monitor LBM).

So, you can add significant strength without adding any muscle. At some point, you will stall and will have to decide whether to eat at a surplus to add muscle or maintain your LBM and strength where it is.

It's up to you of course, but what I would do (or more accurately, what I am doing now) is continue the caloric deficit until I've lost all the fat I want and got to my desired weight. Then after that I can slowly move my calories up to maintenance, and then to a slight surplus, and start putting on strength and muscle.

It's so hard to lose weight and build muscle at the same time it just seems more worthwhile to me to do them separately, rather than trying to do them together and not losing weight as effectively or gain muscle as effectively.

Right but when you do it that way you lose a significant amount of muscle while you're dieting down, and that's really tough to get back. A lot of the point of lifting in a calorie deficit is to keep the muscle you already have instead of losing it along with fat.

I did it the way you're suggesting, and I really wish I hadn't.