The Se5a is still a lethal weapon .... as long as you keep your speed and energy up.
I long ago dropped the idea of "Turn" or "Boom and Zoom" fighters, as it's a road to ruin. All fighters are energy fighters.
The difference is the energy band they work best within. A number of P-51's were lost in Korea attempting to shoot down the ultra uber Po-2 as an extreme example. The Mustang pilots were attempting to shoot them down by flying very low at the limits of stall and manuever against plywood biplanes.
That didn't mean the Po-2 was superior to the Mustang, or that the Mustang was modelled incorrectly.
In WWI planes it can be really dramatic - the Nieuport 11 is a fine aircraft and very lethal as designed when matched against aircraft within the same energy band. However, how it acted within that zone was different depending on its adversary.
Against a Taube the N11 was best served in slashing attacks, as the Taube lived in a lower energy "home" and matching it would put the N11 below its own best performance envelope. Against an Eindecker it could both outclimb and out turn - dealer's choice, as the energy bands weren't that far off. Against the first Albatros it was forced to carefully manage its energy and try to get the Hun to bring his plane down to the N11 energy "home," as it was below where the Albatros best worked at.
The SE5a isn't a dog by any stretch, or inferior. It just has a higher energy level demand than the Pfalz for a host of reasons. The Pfalz driver who's thinking will always try to get the SE5a to expend too much of his energy while staying within his own optimum range.
DR1's, of course, are hilarious and it's clear why they were produced in such small numbers and quickly removed from the front lines. Once a fellow in a peer aircraft realizes it's a one trick pony they're not too much of a threat - the smart English or French pilot that spots one early can dictate the fight. Loads of fun in multiplayer taking a stab at a DR1, flying well out of his gun range, climbing, and either ignoring him as one climbs, letting him chase at ever increasing distances (invariably blowing his energy and making him easy prey for the SPAD he didn't see), or re-engaging. Even in a supposed "dogfight" they're relatively easy to manage if one stays within one's energy band and doesn't try to match their speed.
The flip side is true as well. I shot down the overblown DR1 in single and multiplayer in Nieuport 11's and DH2's by reversing the tactic on them, forcing them to fly too slow in an attempt to match maneuvers. Once they're within five miles an hour of stall they'll either be fair game or forced to dive away - letting the "inferior" aicraft pick up even more energy (airspeed or altitude).