Let me tell you something. I think a pianist needs both. I've been practising on a yamaha electric keyboard, now, for about a month. This is a first for me. I've been working on chopin op. 35. So, a few days ago, I went to visit my friend in Nice who has a kawai grand - a regular size one. Here's what resulted: I could barely get through the scherzo, and the finale came out perfectly. You know why? Because working with an electric keyboard, I had to really "feather" touch the keys to get a piano in the last movement. And it was so uneven. then, when I changed to a regular piano with a resisting touch, it was a cinch. On the other hand, the resistance to something fast and forte, like the scherzo, slows you down. Wow, does it EVER slow you down!
But, I think in the long run, a lightly weighted piano is best. Look at Horowitz. He swore by that type of mechanism for practising. Because it develops sensitivity and variety in your touch. Something similar happened to me way back in the dark ages when I gave my exams at the conservatory in Rome. I had an old upright piano in my apartment which would play by itself if the wind blew in the room. Really really light touch. But when I went for my exams on a concert steinway grand, it felt like driving a Ferrari. It took a few minutes to get used to it, but when I did it was " OMG! Give it the gas baby! Here I come!!!!!"
But I can understand your dilemma. I don't think there's anything you can do with an electric keyboard. You might consider a silent keyboard which are really resistant. However, I think if your teacher has made you this offer, to practise on his piano, I would really insist on it with your parents. Maybe have him talk with them.