I was fully prepared to try tube shocks & pay the fairly high cost of conversion kits. As an experiment, I first tried new top quality lever shocks (actually rebuilt by Peter) with the intention of changing to tubes if needed. The good lever shocks were such an improvement that I didn't bother with the tubes. Plenty of tube shocks were available in the 50's & 60's if Healey had wished to use them. A lever shock can feel pretty good when manually operated but still be way down in damping ability compared to a "good" one.
The good load sensitive adjustable rate tube shocks may be an advantage for all out competition, however the factory race Healeys didn't seem to feel a need for them & they were available then.
IMO, the main advantage of tube shocks on later production cars is that they are considerably cheaper to manufacture, replace, find room for, & require less expensive brackets & no links.
Just like the highly vaunted rack & pinion steering. It's much cheaper to build & to find chassis room for. Not particulary better steering than a good worm & peg system which requires noticeably more parts & space.
Often the newer designs are just cheaper to build. Manufacturing economy has become the number one goal.
I'll get off my soap box now. To each his own.
D