In all the uproar about SC Sea little is said about the capabilities of the countries in the area.
I will exclude Cambodia and Laos because they're too close to China and literally have no military capabilities at all or don't have claims to SC Sea. Brunei with its population of 460,000 and no real military is also excluded.
Vietnam
Fighter: 80 (46 Su-27/30 + 34 Su-22)
AWACS: 0
Subs: 6 (relatively new Kilo)
Frigates: 4 (new Gepard class light frigates)
Missile/ASW equipped Corvettes: 5 (mainly 1990s vintage)
ASuW Fast Attack Craft: 10 (dating to 1980s)
ASW aircraft: 0
ASW helicopters: 8
Long range SAM: 2 x S300PMU batteries, multiple regiments of obsolete S75/125 from 1960s and 1970s.
Malaysia
Fighter aircraft: 26 (8 F/A-18 + 18 Su-30) + 13 subsonic Hawks
AWACS: 0
Subs: 2 (relatively new)
Frigates: 2 (mainly 1990s vintage)
Missile/ASW equipped Corvettes: 6 (mainly 1990s vintage)
ASuW Fast Attack Craft: 8 (dating to 1970s)
ASW aircraft: 0
ASW helicopters: 12
Long range SAM: 0
Indonesia
Fighter aircraft: 49 (16 Su-27/30 + 33 F-16) + 23 subsonic Hawks + 14 T-50 supersonic trainers with limited capability
AWACS: 0
Subs: 4, building up to 8 (new subs but based on old U209 design whilst 2 are based on ancient U206 design and date from early 1980s!)
Frigates: 7 (mainly 1960s vintage ex-Dutch ships based on British Leander class without much in the way of upgrades)
Missile/ASW equipped Corvettes: 24 – mixed bag with some new ships but mainly old ex-East German ships of dubious quality and poor serviceability
ASuW Fast Attack Craft: 15
ASW aircraft: 0
ASW helicopters: 2 (not a typo)
Long range SAM: 0
Philippines
Fighter aircraft: 12 T/A-50 supersonic trainers with some combat capability.
AWACS: 0
(Note up to 1970s Philippine Air Force was one of the most powerful in SE Asia)
Subs: 0
Frigates: 2 (new modern ships)
Missile/ASW equipped Corvettes: 1
ASuW Fast Attack Craft: 0
ASW aircraft: 0
ASW helicopters: 2 (just like Indonesia, also not a typo)
Long range SAM: 0
Singapore
Fighter aircraft: 100 (40 F-15 + 60 F-16). Initial 4 F-35Bs ordered
AWACS: 4
Subs: 4 (being replaced by 4 new ultra advanced Type 218 subs)
Frigates: 6 (new modern ships)
Missile/ASW equipped Corvettes: 6
ASuW Fast Attack Craft: 0
ASW aircraft: 0
ASW helicopters: 8
Long range SAM: 12 Aster 30 launchers being acquired to replace MIM-23
Thailand
Fighter aircraft: 98 (34 x obsolete F-5E/F, 53 X F-16A/B, 11 x JAS-39) + 12 t-50 supersonic trainers
AWACS: 2
Subs: O in service, has ordered 3 Chinese Type S26 subs.
Frigates: 7 (6 older Chinese units plus 1 modern South Korean ship with a second one planned)
Missile/ASW equipped Corvettes: 7 (4 are obsolete)
ASuW Fast Attack Craft: 0
Thailand also has an aircraft carrier, however no fighter aircraft to operate from it following retirement of ancient AV-8S. Current ASuW helicopter fleet is too small to support this and other warships.
ASW aircraft: 1 (a lone ancient P-3 is still serviceable in ASW warfare role)
ASW helicopters: 10 all relatively modern MH-60/Super Lynx
Long range SAM: 0
So as you can see other than Singapore, the rest of SE Asia is incapable of defending itself.
It should be noted most of the militaries in SE Asia are in decline and well past their prime.