ᐅ Is repainting paneled doors too time-consuming?

Hello everyone,
I am currently refurbishing our old panel interior doors and closet doors.

We stripped the doors. The top layer (synthetic resin) came off quite well. Underneath, a kind of white filler putty applied to the wood became visible. I strongly suspect this is original from 1948.

While sanding this coating, I sanded down to the wood in several places. The sales assistant at the specialty store gave me a filler paint to go along with the new acrylic paint, also acrylic-based. I applied this and sanded it lightly again. And what can I say... I am not satisfied with the surface (see photo).

I have now started applying a fine filler thinly.

Now I have spent an entire weekend on ONE SIDE OF ONE DOOR.

Sorry, I accidentally pressed an extra key, and the post was created. Here is the continuation:

I have now spent an entire weekend working on ONE SIDE OF A DOOR and wonder how the professionals do it and whether I should maybe have the job done by someone else.
How do you handle this? I still have 6 doors ahead of me. This won’t work like this...

Here is a photo. You can now clearly see the wood grain where I sanded through.