Thank you all for the input. I'm going for an apron-less table, which is why I wanted the tenons to be spaced apart - so there would be as much of a lever between them as possible as they have to cantilever from the table base to resist racking.
I don't know why but it didn't occur to me to use a saw to cut out most of the piece between the tenons, so I originally did that by chisel. I deepened it a small amount with a saw and it was much easier to remove the waste.
With the mortises I guess it's just a lot of work to cut them out without power tools, and I can't justify the expense of a routing plane for this project - maybe for the next one. On the upside - I have a small right-angled woodcarving tool I can use for the corners.
As for the strength, I cut each leg about 3" longer than needed so I'd have a few attempts on each, and the mortises were cut into a scrap piece - so I decided to load test it. The test was pretty harsh IMO - the joint is my first attempt and didn't fit as snug as I'd like and I only gave the glue 18 hours even though the bottle recommends 24. The tenons are about 11/16" long and I have space to cut them deeper, so for the actual table I'll make them closer to 7/8".
In total the leg carried 45 pounds (didn't get the photo for that one so the pic below only has 40 pounds) and failed when I took the load up to 50#, slowly pulling out over the course of about 5 seconds once it started moving.
Given this is for a small side table and not a dining table that might be abused more I reckon the strength should be OK.