If you hate ladder work (me too) and are willing to do it yourself, look into renting a scaffold. Mine had a generous 3x4 platform for paint tray and walking room, ladder rungs with hand rails on both sides. Easy access to the top, super stable and was perfectly comfortable for hitting the high area of wall in our foyer. Stood there cutting in wall at ceiling and it was eye level, nice! Comes in pieces like a puzzle for transport, just put it together at home. I got one at our local rent-it center for abt $75 for a weekend, or $150 for a week. Way cheaper than hiring it out. Piece of cake to work from. Just wanted to offer a tip for future reference. Every time I paint something I take a fresh wooden stir stick and with a fine tip Sharpie write the manufacturer, date, room, color name/#, sheen and formula. (Abbreviated you can squeeze all that onto half the stick at the handle end, using both sides if necessary. Don't use a fat tip Sharpie, it bleeds too much and is illegible.) Then dip the stirring end of the stick in the paint can (with paint well mixed) so it's covered about half way up but doesn't cover your written info. Set it on edge of can lid with newspaper underneath to catch any drips & let it dry overnight. I keep my painted sticks loosely rubber-banded in a storage box inside the cabinet where my brushes and misc paint sundries are. Takes up little room and you have a ready reference in a case like this, just walk in the store with your stick in hand. (I've found it comes in handy too when shopping for fabrics or other items for the room, painted stick is bigger than a small paint sample and is precisely what was put on your walls.)

Nothing I have ever seen or heard of other than the aerosol.

I'm not sure anything that becomes rigid when dry is going to be a good choice because the way the wood of the wall and floor will expand and contract differently with changes in humidity. I think a color matched caulk would be a better choice. In addition to the "general construction" type caulks you might also want to look at caulks that come the companies that make tile grout. Many of companies offer dozens of colors, maybe you can get lucky there. Frankly you'd be better off using some kind of little wood moulding. There's a reason they invented the stuff...

Had I done this job your complaints (except for the inconsistent stain on the tread) would be covered by the disclaimer "Does not include any touchup painting or a complete dust cleanup" that goes on every proposal. If asked, I will mask off adjacent surfaces but stain and finish often work their way up behind the tape. I also charge more to do so. My position is that if an adjacent surface is just a standard paint, it's cheaper to repaint than to mask off, considering that there still may be some touchup needed. If the adjacent surface is faux finished, stone or finished cabinetry, we will take extra care. Of course that costs more so we charge more. I regularly tell clients not to finish paint before the floor sanding and finishing. We'll be sanding next to vertical surfaces at least twice, then applying finish. Are you sure the finisher didn't tape the base? In one of your pictures the base looks good but the adjacent casing appears to have the issue I mentioned, that the stain wicked up between the tape and the paint. We use dust pickup so generally we don't leave much dust but accidents do happen Like a Trio bag blowing off). We don't charge a penny for dust cleanup and don't do any beyond what is required to get the floor done right. Part of this is because my guys are more expensive than dedicated cleaners (and less skilled) while another part is that fact that we're often among the last people on a job and may be expected to clean up messes from every trade that preceded us without compensation. Contractors here usually hire a professional crew to clean from top to bottom after all the trades are done. A skilled painter shouldn't have any problem touching up your trim. Walls and trim are painted more frequently than floors are finished so this is typically not a challenge.