In rapier we would encounter this problem all of the time: You'd go up against opponents in sparring that were significantly weaker or stronger than you all of the time, and you have to learn to not walk over the weaker opponents so that they could still have a good game and learn something while working on your technique.
First, though, let me say that there is nothing that compares with having someone your own level or stronger to fight. So if you are lacking that in your training, talk to your instructor about ways to fill that gap. When working with weaker opponents, your goal is going to be to help to elevate them to your level or beyond.
In rapier (and currently for me in Hapkido) there were a couple of things that we emphasized when fighting weaker opponents, in particular, that might help:
- Make your technique perfect.
- Limit yourself in some way.
- Do more "at speed" structured drills.
Make your technique perfect
It's really easy to win against a newer fighter with slop. Things you can't get away with against a stronger fighter (or very rarely get away with against a stronger fighter) work beautifully against newer fighters because they haven't seen it before, or because their technique isn't good enough to counter it.
Instead, focus on perfecting your technique. If you throw a kick or a punch, it should be perfectly under your control. It should be placed exactly where you want it (we used to talk about "superior point control," which included the ability to consistently hit someones hand through a swept hilt). It should land with precisely the amount of force you dictate, not any more or less, on precisely the location you want it to.
Work on not telegraphing anything of your own and on reading them perfectly. Work on seeing what they could have done and could be doing that would slip through your guard.
A common one for us right now (given that Hapkido is a self defense art) is to focus on countering. Don't attack them, get out of the way and counterattack only. If you miss or if they get out of the way, reset and wait for their next sequence. You can limit yourself here in the number of attacks you get in reply or in the length of the exchange that you engage in with them.
You can also limit your techniques. See if you can win with nothing but a front kick. Or perhaps with nothing but a front kick off of your non-preferred leg. You might throw other techniques (or not), but the only one you will allow to land is a perfectly placed front kick off of your non-preferred side. You can also focus on techniques you don't feel as comfortable with or aren't as good at.
Another one we used to do is to either anchor your feet or, alternatively, require that you only evade and never block.
A lot of older martial arts have a concept of a "two person form." In Taekwondo (at least for my instructor's students), an element of this is preserved in the one-step (and two step, etc) drills, which you can adapt with the help of the instructor to the purpose if they don't quite fit what you need, or you might modify to work with pads (or hand pads).
The great thing about interactive drills is that they provide an opportunity to do things at a very high degree of intensity, since the other student should know what is coming next and may have something to do when that happens. If you can work with a more advanced student on these drills it may prove particularly valuable, since they can take the hit and will certainly get the block into place.
It also bears mention that when doing drills on your own against a bag or the air you should always strive to do it at full force and with perfect form. Which is itself a great way to improve the intensity of your fighting.