It's fine. I mean the best execute ability is executioner not mages wrath because stam is flat out better than mag if you ask me.
Go for mage wrath if you need it to be ranged. Stam is more effective 2018.
From a PvP perspective (which is all I feel qualified to talk about), this is what the skills have going for them:
Magblade: Impale is decent. It is ranged, which is surprisingly helpful in melee builds, as well as ranged builds. You can hit characters trying to get out of melee range with it. Both Impale and Merciless Resolve will feature in typical end-game PvE DPS builds. In PvP Impale is quite often omitted from builds, since nightblades have another strong burst skill in Merciless Resolve that tends to compete for the same spot on your bar.
Stamblade: Killer's Blade lacks the range, which means it's got strong competition from Executioner / Reverse Slice, if you are running 2H. The splash damage from the latter can be very useful. In PvE Reverse Slice can achieve superb AOE damage on tightly packed mobs, even bashing them from full health. Some people like that Killer's Blade does full execute damage from 25%, whereas other people prefer that Reverse Slash and morphs scale gradually from 50%. Furthermore using an Asylum weapon allows you to generate tons of Ultimate from Reverse Slash, a further point in it's favor. On the other hand you may slot Killer's Blade, if it's the only Assassination ability on the skill bar, to avail of a passive that gives you extra crit damage.
Templar: Only magicka templars have an execute, a 2.8 second ranged beam. This used to be very strong, but I believe the damage has been nerfed to be more in line with other classes. The main advantage of this execute is in group play, in PvP, since you are very visibly "debuffing" a player, which may cause your faction mates to coordinate with you and also attack that player. People hate the "jesus beam" for that reason.
Sorcerer: There is only a magicka execute. Sorcerers tend to have quite a rigid playstyle, with which they generate burst. Burst means several delayed attacks will hit the target at once. A sorc wants to nuke you instantly, but they need to cast several abilities to prepare. The execute is one of them. It effectively puts a bomb on the target, which goes off if the target falls below 20% health in the next 4 seconds. The distinguishing feature is that this execute integrates with the magsorc playstyle. It can also been used to steal kills and generate high scores in Battlegrounds.
Warden: The execute is tied to the Bear ultimate. The bear sucks in PvP and needs to be double-barred. Enough said. I do believe the bear is good in duels, and maybe in PvE, although I believe wardens do not excel as PvE DPS.
DKs don't have an execute.
The weapon executes are Reverse Slash, and morphs, from the 2H line, which is excellent, as discussed in the Stamblade section.
Poison Injection, from the bow skill line, also counts as an execute, for example for the purposes of armor set bonuses that activate on executes. It is a DOT (damage over time) that gets a lot stronger when an enemy is in execute range. Aggressive PvP stamina builds often combine Poison Injection with a melee execute.
Implosion is a 6% proc Chance on a Target below 15% HP though. If it were a set (even a 2pc) I guess no one would use it.