> since e.g. clients would want me for 40 hours per week for a multiyear commitment
I didn't have multiyear/long-term commitment offers often, as in Germany companies are very weary of doing "false self-employment", which comes with hefty fines and hiring a full time freelancer that doesn't have other clients for a year+ is basically the definition of that.
Basically every client I've had, wanted to have me for 40 hours/week, but just like with employment contracts, there is always room for negotiation.
I usually had 2 clients at the same time with optimally 16 hours (= 2 days) each, leaving me with a 4 day work week, but I sometimes budged and gave one of my clients an additional day. If you tell a potential client "I've already given a commitment of 3 days/week to my other client", they normally recognize that there isn't too much wiggle room and from what I can tell generally take it as a sign of professionality that you honor your commitments and can expect the same from you if they are also your client.
The individual gigs were usually 3-6 months and offset with their starting time, so that if one of the 2 gigs runs out, I still have the other one. Once there were 1-2 months remaining on one of the gigs, I hit up my contacts and arranged a new client as a follow-up. That way you have a semi-regular turnover which reduces the pump primed/unprimed problem to some degree. Since I arranged 90% of my jobs through those few freelance contacts I rarely ran into that problem anyway, as the general (unspoken) arrangement with them was that I'm busy by default and they would only ask me if a potential project was really interesting and if I'm looking for a project I'd ping them.
> I think I'd manage this a lot better late career, but on the whole, I found employment to work better for me, at least with a good employer.
The main reason I started freelancing was because from everything I can tell most employers are not good employers, and if they are good employers it's usually a temporary situation that rarely lasts for more than a few years. Most jobs include working on relatively boring products in relatively bad engineering process setups, which is so unfulfilling that I'd at least want to get a good pay/a lot of free time out of it, which always seemed most attainable via freelancing.
Having said that I'm not strictly against employment, and if an interesting employment opportunity with a interesting product and great team comes my way I'm open for it. In fact, I've just started employment again last month, and so far I'm pretty happy with it :)