Are you suggesting the ‘L’ in the EL flash designation is analogous to the L for ‘luxury’ lenses? It’s not.
Nor was it the first Canon EL flash – that was the EL-100, which launched in 2018 (around the time of the EOS R) at $200 and is essentially an upgraded 270EX II with swivel added.
I’d say the EL designation is just Canon’s way of making the nomenclature change obvious. EX flashes replaced EZ-series flashes with the advent of E-TTL metering, and before EZ flashes there was the E-series. That's as far back as my memory goes. For all series prior to the EL series, Canon used a model number based on flash power (e.g. 200E has a GN of 20 m, 430EX has a GN of 43 m, 600EX is 60 m, 90EX is 9 m, etc.).
The EL flashes are numbered like the EOS bodies, where the lower the number, the higher end the flash. Thus, the EL-1 is the flagship/top-of-the-line, and a three-digit number like the EL-100 denotes a consumer level flash. That means the positioning of the EL-5 is similar to that of the R5, a product aimed at advanced enthusiasts and perfectly suitable for professional use, as the 5-series camera bodies have been all along.