@balance
Archer also needs to consume huge amounts of energy just to stay on the same level as the other servants, while you have much stats. Additionally, switching between weapons is the base of Archer's tactics and thus he is a "jack of all trades, master of none" type, each of his Noble Phantasms being low-grade. In addition, you always have 5 offense and 5 speed by default, AND you have abilities that let you raise offense to X (that being the "of charts" overpowered level), AND you have a NP that can defeat any defense and can draw your opponent towards you for free, making Caster useless and Assassin and Rider much weaker.
Let's compare stats a bit.
Max powered Lancer :
-Offense:5 (X for 200 mana per turn)
-Defense:3
-Speed:5
-Endurance:4
-Mana:2
-Spells:3
-Auto-heals for only 100 mana per turn, ignores wounds, mental effects for free, draws opponents to him for free, has magic resistance 4. Pays 50 per turn to keep fighting. 350 mana per turn to fight in full strength. With 3000 mana, can fight at full strength for 8 turns.
Max powered Archer
-Offense:3
-Defense:4 (5 for 300 mp per turn)
-Speed:4 (5 when defense is buffed)
-Endurance:2
-Mana:5
-Spells:1
-Melee damage increase for 300 mana per turn, 400 mana per turn for bonus attacks from animated knives. No way to deal damage to strong defensive opponents except by a very impractical 2000 mana shot, (compared to Lancers 3 rounds of pain for 800 mana), 2 endurance means he is very squishy and NEEDS the flamberge to survive against melee servants. NEEDS sneak attacks to go 1vs1 against the stronger servants, if he doesn't dodge a nuke type attack, he's done for. Pays 1000 mana to stay at max strength. With 5000 mana, can last for 5 turns and immediately turn into spirit form). If he needs to nuke someone, he loses 2000 mana and can only stay full powered for 3 turns. Additionally, he stays squishy due to low endurance and no way to heal or protect against strong magic.
Hell, he needs maybe 300-ish mana per turn to match you at 50 mana per turn.